Electrical components

Abstract

An electrical assembly comprising a plurality of modules (44), each module (44) comprising at least one module switching element (46) and at least one energy storage device (48), wherein the module switching element (46) and the energy storage device (48) in each module (44) are arranged to be combinable to selectively provide a voltage source, each module (44) comprising a discharge circuit, each discharge circuit comprising a discharge switching element (50) and a discharge resistor (52), each discharge switching element (50) being switchable so as to switch the corresponding discharge resistor (52) to the corresponding module (44) ) and switched out of the corresponding module (44), wherein the electrical assembly includes a controller (54), the controller (54) being configured to selectively control the discharge switching element (50) when the module (44) is in a blocking state to modulate each discharge resistor (52) to be switched into and out of the corresponding module (44) in a voltage balancing mode, so that each module (44) simulates a resistance load curve to balance the distribution of voltage among the plurality of modules (44), wherein the resistance load curve includes at least one positive resistance slope.

Description

Technical Field

[0001] The present invention relates to an electrical assembly, preferably for use in high voltage direct current (HVDC) transmission. Background Art

[0002] In HVDC power transmission networks, alternating current (AC) power is typically converted to direct current (DC) power for transmission via overhead lines, submarine cables, and / or underground cables. This conversion eliminates the need to compensate for the AC capacitive loading effects imposed by the power transmission medium (i.e., transmission lines or cables), reduces the cost per kilometer of lines and / or cables, and thus becomes cost-effective when power needs to be transmitted over long distances.

[0003] The conversion between DC power and AC power is used in power transmission networks where it is necessary to interconnect DC and AC networks. In any such power transmission network, a converter is required at each interface between AC and DC power to achieve the required conversion from AC to DC or from DC to AC. Summary of the Invention

[0004] According to a first aspect of the present invention, there is provided an electrical assembly comprising a plurality of modules, each module comprising at least one module switching element and at least one energy storage device, the or each module switching element and the or each energy storage device in each module being arranged to be combinable to selectively provide a voltage source, each module comprising a discharge circuit, each discharge circuit comprising a discharge switching element and a discharge resistor, each discharge switching element being switchable so as to switch a corresponding discharge resistor into and out of a corresponding module, wherein the electrical assembly comprises a controller configured to selectively control the discharge switching elements when the modules are in a blocking state to modulate the switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode, such that each module emulates a resistive load profile to balance the distribution of voltage among the plurality of modules, wherein the resistive load profile comprises at least one positive resistance slope.

[0005] Configuration of modules in a blocking state may occur under certain operating conditions of the electrical assembly.When a module is in a blocking state, the module switching elements are off and the module behaves as a passive circuit where the distribution of voltage between modules is governed by the impedance in the circuit.

[0006] If no additional energy is supplied to the blocked module from an external circuit or network, the energy storage devices are effectively disconnected from the external circuit or network and will release their stored energy independently of one another. However, if energy continues to be supplied to the blocked module from the external circuit or network, the unstable, passive distribution of voltage between the modules may cause the voltages of the modules to drift over time. This, in turn, may cause some of the modules to lose power while other modules in the other modules experience a higher voltage contribution, which may trigger associated overvoltage protection systems and thereby lead to a cascading failure of the modules, potentially damaging a large number of modules.

[0007] By modulating the switching of each discharge resistor into and out of the corresponding module, the simulation of the resistive load curve by each module ensures that, for each energy storage device, the current decreases as the voltage decreases and increases as the voltage increases, preferably achieving a voltage balancing mode at or above a minimum voltage threshold as long as the voltage of the corresponding module is at or above the minimum voltage threshold. This provides a voltage balancing effect that prevents the voltage of the module from drifting over time, thereby ensuring a stable distribution of voltage among the multiple modules.

[0008] In an embodiment of the present invention, the controller can be configured to selectively control the discharge switching element to modulate the switching of each discharge resistor into and out of the corresponding module in the voltage balancing mode so that each discharge resistor presents a simulated resistance higher than its actual resistance.

[0009] In further embodiments of the present invention, the controller may be configured to selectively initiate the voltage balancing mode while the module is entering the blocking state.

[0010] In an embodiment of the present invention, the resistive load curve may include: a single positive resistance slope; multiple positive resistance slopes; or a combination of multiple positive resistance slopes and at least one discontinuity. When the resistive load curve includes multiple resistance slopes, the resistance slopes may be configured so that there is continuity or discontinuity between consecutive resistance slopes. The discontinuity may take the form of a negative resistance slope or a step change. When the resistive load curve includes multiple positive resistance slopes, each positive resistance slope may be the same as or different from the or each other positive resistance slope. When the resistive load curve includes multiple discontinuities, each discontinuity may be the same as or different from the or each other discontinuity. The number of resistance slopes may be varied to provide a more optimized resistive load curve that is better suited to a particular configuration or application of the electrical assembly. For example, the resistive load curve may include multiple positive resistance slopes to balance the distribution of voltage between multiple modules and simultaneously reduce the total power consumption by the discharge resistor.

[0011] In such an embodiment, the controller can be configured to selectively control the discharge switching element to modulate the switching of each discharge resistor into and out of the corresponding module in the voltage balancing mode so as to initiate a transition of the resistance-load curve between consecutive positive resistance slopes when the voltages of all modules in the module are above a predetermined minimum transition voltage. Initiating a transition of the resistance-load curve between consecutive positive resistance slopes in this manner prevents the risk of accelerated drift between the voltages of the modules during the voltage balancing mode.

[0012] In a further embodiment of the present invention, the controller can be configured to selectively control the discharge switching element to modulate the switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode, so as to configure each resistive load profile to counteract the negative impedance characteristics of one or more components of each module that behave as a constant power load. The constant power load behavior of the or each such component (e.g., control electronics) of each module can be the result of the power supply of the or each such component drawing current from the or each corresponding energy storage device in the same module while maintaining a constant voltage and power on one side of the power supply. Such a power supply can be a switch-mode power supply. As a result, when the voltage on the other side of the power supply drops, it draws more current, and vice versa. In this manner, the or each such component of each module behaves as a constant power load.

[0013] However, the constant power load behavior of the or each such component across each module may result in drift between the module voltages, which, as described above, may lead to failure of one or more modules. By configuring the resistive load curve to counteract the negative impedance characteristic described above, the risk of drift between the module voltages may be avoided.

[0014] Optionally, the controller can be configured to selectively control the discharge switching element to modulate switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode so as to configure each resistive load curve according to the physical position of the corresponding module in the electrical assembly.

[0015] One or more environmental factors associated with the physical location of each module in an electrical assembly may exert an unbalanced effect on the distribution of voltages between modules in a blocked state. Because each module has a fixed physical location in the electrical assembly, it becomes possible to predict the degree of imbalance between the module voltages based on their respective physical locations. Therefore, the compensation effect provided by each resistive load curve can be configured based on the physical location of each module in the electrical assembly.

[0016] The electrical resistance of the coolant within a coolant system operatively associated with a plurality of modules can exert an unbalanced effect on the distribution of voltage between the modules in a blocked state. Accordingly, the electrical assembly may include at least one sensor for measuring the conductivity of the coolant operatively associated with each module in the electrical assembly, and the controller may be configured to selectively control the discharge switching element to regulate switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode so as to configure each resistive load curve according to the measured conductivity of the corresponding coolant.

[0017] The electrical assembly can be incorporated into a range of electrical devices. For example, a switching valve may include an electrical assembly according to any of the embodiments described above, or a voltage source converter may include such a valve. The electrical assembly of the present invention can be applied to any other device comprising a plurality of modules, each module comprising at least one module switching element and at least one energy storage device, wherein the module switching element and the energy storage device in the or each module are arranged to be combined to selectively provide a voltage source. Examples of such devices include static synchronous compensators, dynamic braking resistors, and electrical interruption devices (such as isolators, disconnect switches, or circuit breakers).

[0018] According to a second aspect of the invention, there is provided a method of operating an electrical assembly comprising a plurality of modules, each module comprising at least one module switching element and at least one energy storage device, the or each module switching element and the or each energy storage device in each module being arranged to be combinable to selectively provide a voltage source, each module comprising a discharge circuit, each discharge circuit comprising a discharge switching element and a discharge resistor, each discharge switching element being switchable so as to switch a corresponding discharge resistor into and out of a corresponding module, wherein the method comprises the steps of selectively controlling the discharge switching element when the module is in a blocking state to modulate the switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode, so that each module emulates a resistive load curve to balance the distribution of voltage between the plurality of modules, wherein the resistive load curve comprises at least one positive resistance slope.

[0019] The features and advantages of the electrical assembly of the first aspect of the invention and its embodiments apply mutatis mutandis to the method of the second aspect of the invention and its embodiments.

[0020] The method may include selectively controlling the discharge switching element to modulate switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode such that each discharge resistor exhibits a simulated resistance higher than its actual resistance.

[0021] The method may include the step of selectively initiating a voltage balancing mode while the module enters a blocking state.

[0022] In the method of the present invention, the resistive load curve may include: a single positive resistive slope; a plurality of positive resistive slopes; or a combination of a plurality of positive resistive slopes and at least one discontinuity.

[0023] When the resistive load curve includes a plurality of resistive slopes, the resistive slopes may be configured such that there is continuity or discontinuity between consecutive resistive slopes.

[0024] When the resistive load curve includes a plurality of positive resistive slopes, the method may include the step of selectively controlling the discharge switching element to modulate switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode so as to initiate a transition of the resistive load curve between consecutive positive resistive slopes when the voltages of all modules in the module are above a predetermined minimum transition voltage.

[0025] The method may include the steps of selectively controlling the discharge switching element to modulate switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode so as to configure each resistive load curve to offset negative impedance characteristics of one or more components of each module that appear as a constant power load.

[0026] The method may include the steps of selectively controlling the discharge switching element to modulate switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode so as to configure each resistive load curve according to a physical position of the corresponding module in the electrical assembly.

[0027] The method may include the steps of measuring the conductivity of a coolant operatively associated with each module in the electrical assembly; and selectively controlling the discharge switching element to modulate switching of each discharge resistor into and out of the corresponding module in the voltage balancing mode so as to configure each resistive load curve according to the measured conductivity of the corresponding coolant.

[0028] The configuration of each module may vary, non-limiting examples of which are set forth below.

[0029] In a first exemplary configuration of the module, the or each module switching element and the or each energy storage device in the module may be arranged to be combinable to selectively provide a unidirectional voltage source. For example, the module may include a pair of module switching elements connected in parallel with the energy storage device in a half-bridge arrangement to define a two-quadrant unipolar module that can provide either zero voltage or positive voltage and conduct current in both directions.

[0030] In a second exemplary configuration of the module, the or each module switching element and the or each energy storage device in the module may be arranged to be combinable to selectively provide a bidirectional voltage source. For example, the module may include two pairs of module switching elements connected in parallel with the energy storage device in a full-bridge arrangement to define a four-quadrant bipolar module that can provide a negative voltage, zero voltage, or a positive voltage and conduct current in both directions.

[0031] The multiple modules can be connected in series to define a chain-link converter. The structure of the chain-link converter allows for a combined voltage to be built up across the chain-link converter that is higher than the voltage available from each of its individual modules by inserting energy storage devices from multiple modules, each providing its own voltage, into the chain-link converter. In this manner, switching of the or each module switching element in each module causes the chain-link converter to provide a step-variable voltage source. This allows for the generation of a voltage waveform across the chain-link converter using a step approximation. Consequently, the chain-link converter is capable of providing a wide range of composite waveforms.

[0032] The at least one switching element may be a switching element based on a wide bandgap material or a switching element based on a silicon semiconductor. Examples of wide bandgap materials include, but are not limited to, silicon carbide, boron nitride, gallium nitride, and aluminum nitride.

[0033] At least one switching element may include at least one self-commutated switching device. The or each self-commutated switching device may be an insulated gate bipolar transistor (IGBT), a gate turn-off thyristor (GTO), a field effect transistor (FET), a metal oxide semiconductor field effect transistor (MOSFET), an injection enhanced gate transistor (IEGT), an integrated gate commutated thyristor (IGCT), a dual-mode insulated gate transistor (BIGT), or any other self-commutated switching device. The number of switching devices in each switching element may vary depending on the required voltage and current ratings of that switching element.

[0034] At least one switching element may further include a passive current checking element connected in anti-parallel with the or each switching device. The or each passive current checking element may include at least one passive current checking device. The or each passive current checking device may be any device capable of limiting current flow in one direction only, such as a diode. The number of passive current checking devices in each passive current checking element may vary depending on the required voltage and current ratings of that passive current checking element.

[0035] Each energy storage device may be any device capable of storing and releasing energy to selectively provide a voltage, such as a capacitor, a fuel cell, or a battery.

[0036] The configuration of the voltage source converter can vary depending on its operating requirements.

[0037] In an embodiment of the present invention, the voltage source converter may include at least one converter branch and a plurality of modules, the or each converter branch including an electrical assembly according to any one of the embodiments described above, the or each converter branch extending between a first DC terminal and a second DC terminal, the or each converter branch including a first branch portion and a second branch portion separated by an AC terminal, each branch portion including at least one of the modules.

[0038] In a preferred embodiment of the invention, the voltage source converter comprises three converter branches, each of which is connectable via a respective AC terminal to a respective phase of a three-phase AC network. It will be appreciated that the voltage source converter may comprise a different number of converter branches, each of which is connectable via a respective AC terminal to a respective phase of an AC network having a corresponding number of phases.

[0039] It will be appreciated that the use of the terms "first" and "second" and the like in this patent specification is intended merely to help distinguish similar features (e.g., first and second DC terminals, first and second branch portions) and is not intended to indicate the relative importance of one feature over another, unless otherwise specified.

[0040] It is expressly intended that the various aspects, embodiments, examples, and alternatives set forth in the preceding paragraphs and claims and / or the following description and drawings, and in particular individual features thereof, may be employed independently or in any combination within the scope of this application. That is, all embodiments and all features of any embodiment may be combined in any manner and / or combination, unless such features are incompatible. Applicants reserve the right to change any originally filed claim or to file any new claim accordingly, including the right to amend any originally filed claim to depend on and / or incorporate any feature of any other claim, even though not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Preferred embodiments of the present invention will now be described by way of non-limiting examples with reference to the accompanying drawings, in which:

[0042] Figure 1 A voltage source converter according to an embodiment of the present invention is shown;

[0043] Figure 2 and Figure 3 Shown separately Figure 1 Exemplary half-bridge and full-bridge chain-link module configurations of modules of a voltage source converter;

[0044] Figure 4 An exemplary representation of a converter branch is shown, wherein its modules are in a blocking state;

[0045] Figure 5 Show Figure 4 Time variation of the module voltage;

[0046] Figure 6 illustrates current loading for a given module in a blocking state when the module is configured to emulate a resistive load curve having a single positive resistive slope;

[0047] Figure 7 illustrates the switching modulation period and average dissipated power of the discharge resistor of a given module in a blocking state when the module is configured to emulate a resistive load curve having a single positive resistance slope;

[0048] Figure 8 Graphs with and without the compensation effect provided by the simulated resistive load curves Figure 4 Comparison of the time variation of the module voltage;

[0049] Figure 9 illustrates current loading for a given module in a blocking state when the module is configured to simulate a resistive load curve having multiple positive resistive slopes and discontinuities;

[0050] Figure 10 illustrates the switching modulation period and average dissipated power of the discharge resistor of a given module in a blocking state when the module is configured to emulate a resistive load curve having multiple positive resistance slopes and discontinuities;

[0051] Figure 11 and 12 illustrates an exemplary mode of operation of a given module in a blocking state when the module is configured to simulate a resistive load curve having multiple positive resistive slopes and discontinuities;

[0052] Figure 13 illustrates current loading for a given module in a blocking state when the module is configured to emulate a resistive load curve having a single positive resistive slope; and

[0053] Figure 14 Illustrated is the current loading of a given module in a blocking state when the module is configured to emulate a resistive load curve having multiple positive resistive slopes and no discontinuities.

[0054] The drawings are not necessarily to scale and certain features and certain views of the drawings are shown exaggerated in scale or in schematic in the interest of clarity and conciseness. DETAILED DESCRIPTION

[0055] The following embodiments of the present invention are primarily intended for use in HVDC applications, but it will be appreciated that the following embodiments of the present invention are applicable, mutatis mutandis, to other applications operating at different voltage levels. The following embodiments of the present invention are described with reference to AC-DC voltage source converters, but it will be appreciated that the following embodiments of the present invention are applicable, mutatis mutandis, to other types of converters including AC-AC converters and DC-DC converters.

[0056] exist Figure 1 An electrical assembly in the form of a voltage source converter according to an embodiment of the invention is shown in FIG. 2 and generally designated by the reference numeral 20 .

[0057] The voltage source converter 20 includes first and second DC terminals 24, 26 and a plurality of converter branches 28. Each converter branch 28 extends between the first and second DC terminals 24, 26 and includes first and second branch portions 30, 32 separated by a respective AC terminal 34. In each converter branch 28, the first branch portion 30 extends between the first DC terminal 24 and the AC terminal 34, while the second branch portion 32 extends between the second DC terminal 26 and the AC terminal 34.

[0058] In use, the first and second DC terminals 24, 26 of the voltage source converter 20 are connected to a DC network 36, 38 respectively. In use, the AC terminal 34 of each converter branch 28 of the voltage source converter 20 is connected to a respective AC phase of a three-phase AC network 40 via a star-delta transformer arrangement 42. It is envisaged that in other embodiments of the invention, the transformer arrangement 42 may be a star-star transformer arrangement, may be another type of transformer arrangement or may be omitted entirely. The three-phase AC network 40 is an AC power grid 40.

[0059] Each branch portion 30 , 32 comprises a switching valve comprising a chain-link converter defined by a plurality of modules 44 connected in series.

[0060] Each module 44 may vary in topology, examples of which are described below.

[0061] Figure 1 and 2 The structure of an exemplary module 44 in the form of a half-bridge module 44a is schematically shown. The half-bridge module 44a includes a pair of module switching elements 46 and a capacitor 48. Each module switching element 46 of the half-bridge module 44a is in the form of an IGBT connected in parallel with an anti-parallel diode. The pair of module switching elements 46 are connected in parallel with the capacitor 48 in a half-bridge arrangement to define a two-quadrant unipolar module 44a that can provide zero voltage or positive voltage and conduct current in both directions.

[0062] Figure 3 The structure of an exemplary module 44 in the form of a full-bridge module 44b is schematically shown. The full-bridge module 44b includes two pairs of module switching elements 46 and a capacitor 48. Each module switching element 46 of the full-bridge module 44b is in the form of an IGBT connected in parallel with an anti-parallel diode. The pairs of module switching elements 46 are connected in parallel with the capacitor 48 in a full-bridge arrangement to define a four-quadrant bipolar module 44b that can provide negative voltage, zero voltage, or positive voltage and conduct current in both directions.

[0063] The structure of a given module 44 includes the arrangement and type of module switching elements 46 and energy storage devices 48 used in the given module 44. It will be appreciated that it is not necessary for all modules 44 in the module to have the same module structure. For example, multiple modules 44 may include a combination of half-bridge modules 44a and full-bridge modules 44b.

[0064] It is contemplated that, in other embodiments of the present invention, each module switching element 46 of each module 44 may be replaced by a gate turn-off thyristor (GTO), a field effect transistor (FET), a metal oxide semiconductor field effect transistor (MOSFET), an injection enhanced gate transistor (IEGT), an integrated gate commutated thyristor (IGCT), a dual-mode insulated gate transistor (BIGT), or any other self-commutated semiconductor device. It is also contemplated that, in other embodiments of the present invention, each diode may be replaced by a plurality of diodes connected in series.

[0065] The capacitor 48 of each module 44 is selectively bypassed or inserted into the corresponding chain-link converter by changing the state of the module switching element 46. This selectively directs current through or bypasses the capacitor 48, causing the module 44 to provide zero or non-zero voltage.

[0066] When the module switching element 46 in the module 44 is configured to form a short circuit in the module 44, the capacitor 48 of the module 44 is bypassed, thereby short-circuiting the bypass capacitor 48. This causes the current in the corresponding chain-link converter to pass through the short circuit and bypass the capacitor 48, and thus the module 44 provides zero voltage, i.e., the module 44 is configured in the bypass mode.

[0067] When the module switching element 46 in the module 44 is configured to allow current in the corresponding chain-link converter to flow into and out of the capacitor 48, the capacitor 48 of the module 44 is inserted into the corresponding chain-link converter. The capacitor 48 then charges or discharges its stored energy to provide a positive voltage, i.e., the module 44 is configured in the non-bypass mode.

[0068] In this manner, the module switching element 46 in each module 44 is switchable to control the flow of current through the corresponding capacitor 48 .

[0069] By inserting the capacitors of multiple modules 44, each providing its own voltage, into each chain-link converter, it is possible to accumulate a combined voltage across each chain-link converter that is higher than the voltage available from each of its individual modules 44. In this manner, the switching of the module switching elements 46 in each module 44 enables each chain-link converter to provide a step-variable voltage source that allows a voltage waveform to be generated across each chain-link converter using a step-wise approximation. Thus, the module switching elements 46 in each branch portion 30, 32 can be switched to selectively allow and prevent the flow of current through the corresponding capacitor 48 in order to control the voltage across the corresponding branch portion 30, 32.

[0070] It is envisaged that in other embodiments of the invention, each module 44 may be replaced by another type of module comprising at least one module switching element and at least one energy storage device, the or each module switching element and the or each energy storage device in each such module being arranged to be combinable to selectively provide a voltage source.

[0071] It is also contemplated that in other embodiments of the present invention, the capacitor 48 in each module 44 may be replaced by another type of energy storage device capable of storing and releasing energy to provide a voltage, such as a battery or fuel cell.

[0072] Each module 44 also includes a discharge circuit in the form of a series connection of a discharge switching element 50 and a discharge resistor 52. In each module 44, the series connection of the discharge switching element 50 and the discharge resistor 52 is connected in parallel with the capacitor 48 so that the discharge switching element 50 can be switched to switch the discharge resistor 52 into and out of the module 44. Each discharge circuit can be used to provide a rapid discharge capability for the corresponding module 44.

[0073] It is contemplated that in other embodiments of the present invention, the discharge switching elements and the discharge resistors may be arranged differently in the discharge circuit. It is also contemplated that in still other embodiments of the present invention, the discharge circuit may include a different number of discharge switching elements and / or a different number of discharge resistors.

[0074] The voltage source converter further includes a controller 54 that is configured (eg, programmed) to control switching of the module switching element 46 and the discharge switching element 50 .

[0075] For the purpose of simplicity, the controller 54 is exemplarily described with reference to its implementation as a single control unit. In other embodiments, the controller 54 may be implemented as multiple control units. The configuration of the controller 54 may vary depending on the specific requirements of the voltage source converter 20. For example, the controller 54 may include multiple control units, each of which is configured to control the switching of the module switching element 46 of a corresponding module in the modules 44. Each control unit may be configured to be inside or outside the corresponding module 44. Alternatively, the controller may include a combination of one or more control units inside the corresponding module 44 and one or more control units outside the corresponding module 44. Each control unit may be configured to communicate with at least one other control unit via a telecommunications link.

[0076] Each module 44 also includes a bleeder resistor 56 connected in parallel with the capacitor 48 and the discharge circuit. In each module 44, the bleeder resistor 56 typically has a higher ohmic value than the discharge resistor 52. For example, in each module 44, the bleeder resistor 56 typically has a value of several hundred ohms. The ohmic value of the discharge resistor 52 ranges from to a few Preferably, the discharge resistor 52 has an ohmic value such that it can draw a current comparable to the load current of the voltage source converter 20 itself, which may be in the range of 1000 A to 2000 A. This enables the discharge resistor 52 to be used for fast discharge.

[0077] Operation of the voltage source converter 20 Figures 4 to 14 Description is as follows.

[0078] To transfer power between the DC and AC networks 36, 38, 40, the controller 54 controls the switching of the module switching elements 46 of the modules 44 to switch the capacitors 48 of the corresponding branch sections 30, 32 into and out of the circuit between the corresponding DC and AC terminals 24, 26, 34 to interconnect the DC and AC networks 36, 38, 40. The controller 54 switches the module switching elements 46 of the modules 44 of each branch section 30, 32 to provide a step-variable voltage source between the corresponding DC and AC terminals 24, 26, 34 and thereby generate a voltage waveform to control the configuration of the AC voltage waveform at the corresponding AC terminal 34 to facilitate power transfer between the DC and AC networks 36, 38, 40.

[0079] During normal operation of the voltage source converter 20 , the modules 44 operate in a deblocking state, with the module switching elements 46 being switched to maintain a balanced distribution of voltage among the modules 44 within each power cycle.

[0080] Each module 44 can be switched to a blocking state in which the module switching element 46 is off and each module 44 behaves as a passive circuit in which the distribution of voltage between modules 44 is governed by the impedance in the circuit. Figure 4 An exemplary representation of a converter branch 28 is shown with its modules 44 in a blocking state, with a DC voltage applied across the modules 44 .

[0081] The configuration of the modules 44 in the blocking state may occur for a very short period, typically a few seconds, at start-up of the voltage source converter 20, during which energy is supplied to the voltage source converter 20 from the DC network 36, 38 or the AC network 40 in order to pre-charge the capacitors 48. The configuration of the modules 44 in the blocking state may also occur during shutdown of the voltage source converter 20, wherein the capacitors 48 are typically slowly discharged over the course of several minutes. During shutdown of the voltage source converter 20, no further energy is supplied to the blocked modules 44 from the DC network 36, 38 or the AC network 40, which results in the capacitors 48 being effectively disconnected from the DC and AC networks 36, 38, 40 and releasing their stored energy independently of each other.

[0082] In the event that a module 44 is in a blocked state and energy continues to be supplied to the blocked module 44 from the DC network 36, 38, the AC network 40, or both networks 36, 38, 40, the unstable passive distribution of voltages between the modules 44 may result in a drift between the voltages of the modules 44 over time, such as Figure 5 As shown in . Figure 5 Starting on the left hand side of the graph in , the sum of the voltages of the modules 44 in the voltage source converter 20 exceeds the voltage applied to the voltage source converter 20 from the DC and / or AC network 36, 38, 40, which means that energy is not supplied from the DC and / or AC network 36, 38, 40 to the blocked module 44. As a result, the capacitors 48 of the modules 44 all discharge independently at substantially the same rate. Figure 5 At the point in time indicated by 'A' in FIG, the sum of the voltages of the modules 44 in the voltage source converter 20 drops below the voltage applied to the voltage source converter 20 from the DC and / or AC network 36, 38, 40, which means that energy is now fed from the DC and / or AC network 36, 38, 40 to the blocked module 44. Thereafter, the voltages of the modules 44 begin to diverge, resulting in an imbalance between the voltages of the modules 44. This in turn may result in some of the modules 44 being de-energized while some other modules 44 in other modules have a higher voltage contribution, which may trigger an associated overvoltage protection system and thereby result in a cascading failure of the modules 44, potentially damaging a large number of the modules 44.

[0083] During normal operation of a point-to-point HVDC power transmission scheme, the risk of drift over time between the voltages of the blocked modules 44 may be neglected because energy is supplied to the blocked modules 44 for only a few seconds during start-up of the voltage source converter 20, and because the relatively large size of the capacitors 48 means that divergence between the voltages of the blocked modules 44 may take several minutes to occur. However, there may be certain normal and fault operating conditions of the voltage source converter 20 that may require the modules 44 to be in a blocked state and connected to the DC network 36, 38, the AC network 40, or both networks 36, 38, 40 for an extended or indeterminate period of time.

[0084] Because the control electronics of a blocked module 44 presents a constant power load CPL, voltage drift over time in the blocked module 44 may occur. Specifically, in each module 44, the control electronics presents a constant power load CPL because the switch-mode power supply of the control electronics draws current from the corresponding capacitor 48. The high-voltage side of the switch-mode power supply is connected to the corresponding capacitor 48. The switch-mode power supply naturally attempts to maintain a constant voltage and power on its low-voltage side. As a result, when the voltage on the high-voltage side of the power supply drops, it draws more current, and when the voltage on the high-voltage side of the power supply rises, it draws less current. Therefore, when the voltage of the corresponding capacitor 48 decreases, the switch-mode power supply draws a higher current, and when the voltage of the corresponding capacitor 48 increases, the switch-mode power supply draws a lower current. This results in the control electronics of each module 44 exhibiting a negative impedance characteristic, which in turn causes drift between the voltages of the blocked modules 44 due to energy supply from the DC network 36, 38, the AC network 40, or both networks 36, 38, 40. At a certain voltage of the capacitor 48 , the constant power load CPL disappears because the control electronics are powered down due to the switch mode power supply operating only at or above a certain minimum voltage of the capacitor 48 .

[0085] The risk of drift between the voltages of the modules 44 can be avoided by enabling each blocked module 44 to change its load profile by simulating a resistive load profile that counteracts the negative impedance characteristics of the control electronics of each blocked module 44, which presents a constant power load. The resistive load profile of each module 44 can be simulated by switching the discharge switching element 50 to switch each discharge resistor 52 into and out of the corresponding module 44 in a voltage balancing mode, preferably with a low duty cycle modulation, so that each discharge resistor 52 presents a higher resistance than its actual resistance. Simulated resistance .

[0086] The modulation of each discharge resistor 52 switching into and out of the corresponding module 44 preferably involves fixing the on-time of the corresponding discharge switching element 50 The modulation period T is adjusted as needed (for example, to tens of seconds) to obtain the desired simulated resistance load curve for each module 44. For an ohmic value of the discharge resistor 52 in the range of 1Ω to 2Ω, the on time It can be dozens , for example 100 For larger ohmic values of the discharge resistor 52, the on-time Will be correspondingly longer.

[0087] Demand reference current for a given module 44 is given as:

[0088]

[0089] in is the initial current of module 44 at the beginning of the voltage balancing mode, v is the instantaneous voltage of module 44, is the minimum voltage threshold of module 44, at and above which the voltage balancing mode is achieved, and is the resistance slope of the simulated resistive load curve of module 44 .

[0090] The current of the discharge resistor 52 By taking the reference current from the demand Subtract the load current drawn by the bleeder resistor 56 and the control electronics of the module 44 from the current to calculate:

[0091]

[0092] The load current drawn by the bleeder resistor 56 is given by is given by, and the load current drawn by the control electronics of module 44 is given by given.

[0093] The current of the discharge resistor 52 is never negative, and for , equation (2) should be constrained to be 0.

[0094] Since the simulated resistance of the discharge resistor 52 Depend on Given, and by and Select the appropriate duty cycle d to obtain, so the modulation period T is calculated as follows:

[0095]

[0096] Assume that the ohmic value of the discharge resistor 52 is sufficiently low (eg, several Ω), since the on-time of the discharge switching element 50 is Significantly smaller than the modulation period T , so the off time of the discharge switching element 50 is It can be assumed to be substantially the same as the modulation period T About disconnection time The same assumption of may or may not apply to larger ohmic values of the discharge resistor 52 .

[0097] The calculation of the modulation period T can be enhanced, for example by firmware, by limiting its excursion to specified minimum and maximum values. This is to prevent the execution of equation (4) which yields an infinite number of values of T that are then negative.

[0098] Preferably, the voltage balancing mode is configured so that it starts functioning as soon as the module 44 enters the blocking state, more preferably, it starts functioning at the same time as the module 44 enters the blocking state. Whenever the module 44 is in the blocking state, the voltage balancing mode preferably remains at the minimum voltage threshold or above the minimum voltage threshold accomplish.

[0099] In voltage balancing mode, the minimum voltage threshold of each module 44 is Can be Exemplarily defined, where VDC is the inter-pole DC voltage across the first and second DC terminals 24, 26 of the voltage source converter 20, and is the number of modules in a given converter branch 28 .

[0100] Minimum voltage threshold Preferably, it is at least equal to the voltage at which the control electronics start up, i.e. higher than the voltage at which the control electronics of each module 44 are powered down. More preferably, in order to reduce power consumption, the voltage of the module 44 will be higher than the minimum voltage threshold as soon as the DC and / or AC network 36, 38, 40 starts feeding energy into the voltage source converter 20. , minimum voltage threshold May be higher than the voltage at which the control electronics start up.

[0101] Optionally, at the point where the DC and / or AC network 36, 38, 40 starts feeding energy to the voltage source converter 20 (as determined by Figure 5 Indicated by 'A' in the may be lower than the lowest possible voltage of each module 44. Although the voltage balancing mode does not have any balancing effect until a point in time when the sum of the voltages of the modules 44 in the voltage source converter 20 drops below the voltage applied to the voltage source converter 20 from the DC and / or AC network 36, 38, 40, initiating the voltage balancing mode before that point in time makes it easier to control the voltage balancing mode.

[0102] Figure 6 The current loading of a given module 44 in a blocked state with a capacitor voltage is illustrated when the blocked module 44 is configured to simulate a resistive load curve. Dashed lines 58, 60 indicate the load current drawn by the control electronics of the module 44 and the bleeder resistor 56, respectively. Dashed line 62 indicates the sum of the load currents drawn by the control electronics of the module 44 and the bleeder resistor 56. The simulated resistive load curve for the discharge resistor 52 is given by the solid line 64 and is plotted from a minimum voltage threshold indicated by diamond marker 66. Start. The dotted line 68 indicates the current of the discharge resistor 52 . Will understand, Figure 6 The x-axis of has a suppressed zero, which is why the load current 58 drawn by the bleeder resistor 58 is shown as having a non-zero value as it crosses the y-axis. Minimum Voltage Threshold is set to the same starting voltage as the control electronics indicated by the triangular mark 69 .

[0103] Figure 7 Figure 4 illustrates the modulation period T of the discharge resistor 52 with the capacitor voltage and the corresponding average dissipated power when the blocked module 44 is configured to simulate a resistive load curve. The modulation period is indicated by line 70 and the corresponding dissipated power is indicated by line 72 .

[0104] Average power dissipation of the discharge resistor 52 It can be calculated as follows:

[0105]

[0106] in .

[0107] Preferably, the resistance slope of the simulated resistance load curve The value is selected (for example, it is selected to be between 100 to 500 range) to produce a slightly rising resistance slope. The value of may be adjusted to account for the leakage resistance of the cooling system associated with module 44 , as detailed later in this specification.

[0108] By modulating the switching of each discharge resistor 52 into and out of the corresponding module 44, the simulation of the resistive load curve by each blocked module 44 ensures that for each capacitor 48, as long as the voltage of the corresponding module 44 is equal to or above the minimum voltage threshold , the current decreases as the voltage decreases and increases as the voltage increases, at the minimum voltage threshold or above the minimum voltage threshold , achieving a voltage balancing mode. This provides a voltage balancing effect that prevents drift between the voltages of the blocked modules 44 and thereby ensures a stable distribution of voltages between the blocked modules 44 over time. Figure 8 The top graph of FIG illustrates the drift between the voltages of the blocked module 44 when the compensation effect of the simulated resistive load curve is not applied, while Figure 8 The bottom graph of illustrates the balancing of the voltages of the blocked module 44 when applying the compensation effect of the simulated resistive load curve.

[0109] Alternatively, the simulated resistive load curve may include multiple resistive slopes. The number of resistive slopes may be varied to provide a more optimized resistive load curve that is more suitable for a particular configuration or application of the voltage source converter 20.

[0110] Figure 9 The diagram illustrates the current loading of a given module 44 in a blocked state with a capacitor voltage when the blocked module 44 is configured to simulate a resistive load curve having two positive resistive slopes and a discontinuity therebetween. The discontinuity is arranged between the two positive resistive slopes so that the three slopes combine to define a discontinuous resistive slope. In the embodiment shown, the discontinuity takes the form of a step change, but in other embodiments may instead take the form of a negative resistive slope. Each positive resistive slope may be the same as or different from the other positive resistive slopes. Dashed lines 74, 76 indicate the load current drawn by the control electronics of the module 44 and the bleeder resistor 56, respectively. Dashed line 78 indicates the sum of the load current drawn by the control electronics of the module 44 and the bleeder resistor 56. The simulated resistive load curve for the discharge resistor 52 is given by the solid line 80 and is obtained from a minimum voltage threshold indicated by the diamond mark 82. Start. The dotted line 84 indicates the current of the discharge resistor 52 . Will understand, Figure 9 The x-axis of has a suppressed zero, which is why the load current 74 drawn by the bleeder resistor 58 is shown as having a non-zero value as it crosses the y-axis. is set to the same as the starting voltage of the control electronics, which is indicated by the triangular marking 85 .

[0111] Figure 10Graph showing the modulation period T of the discharge resistor 52 with the capacitor voltage and the corresponding average dissipated power when the blocked module 44 is configured to simulate a resistive load curve having two positive resistive slopes and a discontinuity therebetween. The modulation period is indicated by line 86 and the corresponding dissipated power is indicated by line 88 .

[0112] Using equation (4), using two different disconnection times Each of the positive resistance slopes is calculated, equation (4), based on two different calculations of the equivalent current in equation (1). The selection between the positive resistance slopes depends on the voltage of the capacitor 48 of the module 44 at a given point in time. Figure 9 The resistive load curve of 44 provides a balancing effect on the distribution of voltage between the blocked modules 44 and at the same time Figure 6 The total power dissipated in each discharge resistor 52 is reduced compared to the resistive load curve for the positive resistor. The transition point between the positive resistance slopes can be varied depending on the voltage balance and power dissipation requirements of the blocked module 44.

[0113] When the voltage of all of the modules 44 is above a predetermined minimum transition voltage, taking into account any associated hysteresis, the controller 54 switches the discharge switching elements 50 to modulate the switching of each discharge resistor 52 into and out of the corresponding module 44 in a voltage balancing mode to initiate a transition of each resistive load curve between successive positive resistance slopes. Figure 9 , where a transition is indicated by a discontinuity 90 between consecutive positive resistance slopes. Initiating a transition of the resistive load curve between consecutive positive resistance slopes in this manner prevents the risk of accelerated drift between the voltages of the modules 44. In contrast, if the voltage of one or more modules 44 is below the transition voltage at which the transition between consecutive positive resistance slopes is initiated, the voltage of the or each such module 44 will quickly collapse toward zero. To ensure that a transition between consecutive positive resistance slopes is initiated only when the voltage of all modules 44 in the module 44 is above the transition voltage, the controller 54 must remain fully active and capable of monitoring the voltage of the capacitors 48 of all modules 44 in the module 44.

[0114] In embodiments of the present invention employing a resistive load curve having multiple positive resistance slopes and at least one discontinuity (step change or negative resistance slope) therebetween, controller 54 may be configured to operate module 44 in the following exemplary modes.

[0115] exist Figure 11In the exemplary first mode shown in FIG, each module 44 is configured to have a resistive load curve comprising two positive resistance slopes AB and CD connected via a negative resistance slope BC. In other embodiments, the negative resistance slope BC may be replaced by a step change. Each of regions AB and CD may consist of a single positive resistance slope, or may consist of multiple positive resistance slopes without any discontinuity therebetween.

[0116] At the time when the modules 44 are reconnected to, and thus powered by, the associated electrical networks 36, 38, 40, all modules 44 in a given switching valve are preferably located in either region AB or region CD, i.e., all modules 44 in a given switching valve are located on the same side of the discontinuity. In the first case, when the blocked modules 44 are powered by the AC network 40, the modules 44 are located in region CD. In the second case, when the blocked modules 44 are powered by the DC network 36, 38, the modules 44 are located in region AB. This is because the average voltage to which the capacitors 48 stabilize is different for the two cases. Typically, the average voltage to which the capacitors 48 stabilize for the first AC excitation case is twice the average voltage to which the capacitors 44 stabilize for the second DC supply case.

[0117] Thus, the first mode enables a given switching valve to autonomously perform a voltage balancing mode by configuring all of its modules 44 to follow the same resistive load curve, without requiring any input from the central control unit. The reliability of the switching valve's autonomous voltage balancing mode can be improved by selecting the appropriate location and value of the discontinuity BC in the resistive load curve.

[0118] exist Figure 12 In the exemplary second mode shown in FIG, each module 44 is configured to have a "default" positive resistance slope and an "eco" positive resistance slope. Operation of each module 44 will typically begin with the "default" positive resistance slope. In the event that the controller 54 identifies that all of the modules 44 are above a certain minimum level corresponding to a level at which a constant power load begins to dominate the total current draw, the controller 54 may send a "shift" command to all of the modules 44 to switch from the "default" positive resistance slope to the "eco" positive resistance slope, wherein the transition between the positive resistance slopes takes the form of a discontinuity 124. Figure 12 Regions 126 in FIG. 4 indicate unsafe operating regions for each module 44 .

[0119] Figure 13The current loading of a given module 44 in a blocked state with a capacitor voltage is illustrated when the blocked module 44 is configured to simulate a resistive load curve having a single positive resistance slope. Dashed lines 92, 94 indicate the load current drawn by the control electronics of the module 44 and the bleeder resistor 56, respectively. Dashed line 96 indicates the sum of the load currents drawn by the control electronics of the module 44 and the bleeder resistor 56. The simulated resistive load curve for the discharge resistor 52 is given by the solid line 98 and is obtained from a minimum voltage threshold indicated by diamond marker 100. Start. The dotted line 102 indicates the current of the discharge resistor 52 . Will understand, Figure 13 The x-axis of has a suppressed zero, which is why the load current 92 drawn by the bleeder resistor 58 is shown as having a non-zero value as it crosses the y-axis. is set to be higher than the start-up voltage of the control electronics indicated by the triangular mark 104. As mentioned above, this approach has the benefit of reducing power consumption.

[0120] Figure 14 1 shows the current loading of a given module 44 in a blocked state with a capacitor voltage when the blocked module 44 is configured to simulate a resistive load curve having two positive resistive slopes with no discontinuity therebetween. The two positive resistive slopes combine to define a continuous resistive slope. The first positive resistive slope is steeper than the second positive resistive slope. Dashed lines 106, 108 indicate the load current drawn by the control electronics of the module 44 and the bleeder resistor 56, respectively. Dashed line 110 indicates the sum of the load current drawn by the control electronics of the module 44 and the bleeder resistor 56. The first positive resistive slope of the simulated resistive load curve for the discharge resistor 52 is given by the continuous line 112 and is plotted from a minimum voltage threshold indicated by diamond marker 114. The second positive resistance slope of the simulated resistive load curve for the discharge resistor 52 is given by a continuous line 118 and starts at the transition voltage indicated by the circular marker 116. The dotted line 120 indicates the current of the discharge resistor 52. . Will understand, Figure 14 The x-axis of has a suppressed zero, which is why the load current 106 drawn by the bleeder resistor 58 is shown as having a non-zero value as it crosses the y-axis. is set to the same as the starting voltage of the control electronics indicated by the triangular mark 122 .

[0121] Figure 14The configuration of two positive resistance slopes 112, 118 in the resistance load curve improves efficiency at higher voltages. It is contemplated that the control unit of each module 44 can be configured to autonomously control the corresponding module 44 to emulate such a resistance load curve without requiring commands from a central control unit.

[0122] In addition to or in lieu of the imbalance effect introduced by the constant power load behavior of the control electronics of the blocked modules 44, the resistance of the coolant within the coolant system (e.g., coolant piping) operatively associated with the modules 44 may exert an imbalance effect on the distribution of voltages between the blocked modules 44, which may result in undesirable drift between the voltages of the modules 44. Because each module 44 has a fixed physical position within the voltage source converter 20, it becomes possible to use their physical position to predict the degree of imbalance between the voltages of the blocked modules 44 caused by leakage resistance. Therefore, the resistance load curve of each module 44 can be adjusted based on the physical position of each module 44 to provide correspondingly different degrees of compensation for the leakage resistance associated with each module 44. Optionally, the voltage source converter 20 can include one or more sensors that measure the conductivity of the coolant and transmit the measured conductivity to the controller 54, with the controller being used to configure each resistance load curve based on the measured coolant conductivity.

[0123] If the controller 54 includes firmware that controls the modulation of switching each discharge resistor 52 into and out of the corresponding module 44 in voltage balancing mode, corresponding different firmware settings can be preloaded in the controller 54 for each module 44 to provide the above-mentioned functionality of compensating for the leakage resistance associated with each module 44.

[0124] Unless the context indicates otherwise, preferences and options for a given aspect, feature or parameter of the invention are to be considered disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention.

Claims

1. An electrical assembly comprising a plurality of modules (44), each module (44) comprising at least one module switching element (46) and at least one energy storage device (48), each module switching element (46) and each energy storage device (48) in each module (44) being arranged to be combinable to selectively provide a voltage source, each module (44) comprising a discharge circuit, each discharge circuit comprising a discharge switching element (50) and a discharge resistor (52), each discharge switching element (50) being switchable so as to switch a corresponding discharge resistor (52) into a corresponding module (44) and The electrical assembly includes a controller (54) configured to selectively control the discharge switching element (50) when the module (44) is in a blocking state to modulate the switching of each discharge resistor (52) into and out of the corresponding module (44) in a voltage balancing mode so that each module (44) emulates a resistive load curve to balance the distribution of voltage among the plurality of modules (44), wherein the resistive load curve includes at least one positive resistance slope.

2. The electrical assembly according to claim 1, wherein The controller (54) is configured to selectively control the discharge switching element (50) to modulate the switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so that each discharge resistor (52) exhibits a simulated resistance that is higher than its actual resistance.

3. The electrical assembly according to claim 1, wherein: The controller (54) is configured to selectively initiate the voltage balancing mode while the module (44) enters the blocking state.

4. The electrical assembly according to claim 1, wherein: The resistive load curve includes: a single positive resistive slope, multiple positive resistive slopes; or a combination of multiple positive resistive slopes and at least one discontinuity.

5. The electrical assembly according to claim 4, wherein: The resistive load curve includes a plurality of resistive slopes configured such that there is continuity or discontinuity between consecutive resistive slopes.

6. The electrical assembly according to any one of claims 1 to 5, wherein: The resistive load curve includes a plurality of positive resistance slopes, and the controller (54) is configured to selectively control the discharge switching element (50) to modulate switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so as to initiate a transition (90) of the resistive load curve between consecutive positive resistance slopes when the voltage of all of the modules (44) is above a predetermined minimum transition voltage.

7. The electrical assembly according to any one of claims 1 to 5, wherein: The controller (54) is configured to selectively control the discharge switching element (50) to modulate switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so as to configure each resistive load curve to counteract negative impedance characteristics of one or more components of each module (44) that present a constant power load (CPL).

8. The electrical assembly according to any one of claims 1 to 5, wherein: The controller (54) is configured to selectively control the discharge switching element (50) to modulate switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so as to configure each resistive load curve according to the physical position of the corresponding module (44) in the electrical assembly.

9. An electrical assembly according to any one of claims 1 to 5, comprising at least one sensor for measuring the conductivity of a coolant operatively associated with each module (44) in the electrical assembly, wherein the controller (54) is configured to selectively control the discharge switching element (50) to modulate the switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so as to configure each resistive load curve according to the measured conductivity of the corresponding coolant.

10. A switching valve comprising the electric assembly according to any one of claims 1 to 9.

11. A voltage source converter (20) comprising the switching valve according to claim 10.

12. A method of operating an electrical assembly comprising a plurality of modules (44), each module (44) comprising at least one module switching element (46) and at least one energy storage device (48), each module switching element (46) and each energy storage device (48) in each module (44) being arranged to be combinable to selectively provide a voltage source, each module (44) comprising a discharge circuit, each discharge circuit comprising a discharge switching element (50) and a discharge resistor (52), each discharge switching element (50) being switchable to switch a corresponding discharge resistor (52) into and out of a corresponding module (44), wherein the method comprises the following steps: When the modules (44) are in a blocking state, the discharge switching elements (50) are selectively controlled to modulate switching of each discharge resistor (52) into and out of the corresponding module (44) in a voltage balancing mode, such that each module (44) emulates a resistive load curve to balance the distribution of voltage among the plurality of modules (44), wherein the resistive load curve includes at least one positive resistance slope.

13. The method according to claim 12, comprising the steps of: The discharge switching element (50) is selectively controlled to modulate the switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so that each discharge resistor (52) exhibits a simulated resistance that is higher than its actual resistance.

14. The method according to claim 12, comprising the steps of: The discharge switching element (50) is selectively controlled to modulate switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so as to configure each resistive load curve to counteract negative impedance characteristics of one or more components of each module (44) that present a constant power load (CPL).

15. The method according to any one of claims 12 to 14, comprising: selectively controlling the discharge switching element (50) to modulate the switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode so as to configure each resistive load curve according to the physical position of the corresponding module (44) in the electrical assembly; and / or the step of measuring the conductivity of a coolant operatively associated with each module (44) in the electrical assembly; and selectively controlling the discharge switching element (50) to modulate switching of each discharge resistor (52) into and out of the corresponding module (44) in the voltage balancing mode to configure each resistive load curve according to the measured conductivity of the corresponding coolant.

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