Power converter

The present disclosure relates to a power converter for use in a host vehicle. The power converter comprises a DC link, a DC link capacitor, and a pre-charge circuit configured to charge the DC link capacitor. The pre-charge circuit comprises a boost converter comprising a switch and inductor coupling terminals configured to couple to an inductive component external to the power converter.

FIELD OF THE INVENTION

The present disclosure relates to a power converter for use in a host vehicle.

BACKGROUND

A transport climate control system is generally used to control one or more environmental conditions such as temperature, humidity, air quality, or combinations thereof, of a transport unit. Examples of transport units include, but are not limited to a truck, a container (such as a container on a flat car, an intermodal container, a marine container, a rail container, etc.), a box car, a semi-tractor, a bus, or other similar transport unit. A transport climate control system may be integrated into the transport unit, or may be provided as a separate transport climate control unit (CCU) that can be mounted or coupled to the transport unit.

A transport climate control system typically includes (among other elements) temperature control components such as pumps, fans, heat exchangers and the like, together with associated electrical elements such as sensors (e.g. temperature sensors), a controller, a display unit, electrical drives, electrical filters and the like. The temperature control components and associated elements are typically electrically powered. The transport climate control system may thus include one or more batteries for supplying electrical power to the temperature control components and associated electrical elements.

Additionally, the transport climate control system may be configured to receive electrical power from the transport unit. For example, the transport climate control system may be configured to receive electrical power from a prime mover of the transport unit (e.g. an engine of a truck, tractor unit or the like), from a battery of the transport unit (e.g. a battery of a truck, tractor unit or the like), and/or from a utility power or “shore power” source such as an electrical grid two which the transport unit can be coupled to receive mains electricity.

SUMMARY

According to a first aspect, the invention provides a power converter for use in a host vehicle, the power converter comprising:a DC link;a DC link capacitor; anda pre-charge circuit configured to charge the DC link capacitor,wherein the pre-charge circuit comprises a boost converter comprising a switch and inductor coupling terminals configured to couple to an inductive component external to the power converter.

The inductive component may comprise an inductive component of the host vehicle, for example.

Alternatively, the inductive component may comprise an inductive component of a climate control unit coupled to the host vehicle.

The inductive component may comprise a motor and/or generator.

The inductive component may comprise a stator winding of the motor or generator.

The host vehicle or the climate control unit may comprise a converter for providing a supply voltage to the motor, and the switch may be provided by a switch of the converter.

The power converter may comprise a voltage source converter.

The power converter may comprise a voltage source converter or a voltage source inverter with an implicit diode rectifier.

The power converter may comprise a two-level converter, a three-level converter or a modular multi-level converter, for example.

The power converter may be operable to convert from AC to DC and/or from DC to AC

The power converter may be operable in a second mode to convert between an input DC voltage at a first magnitude and an output DC voltage at a second magnitude.

The power converter may be operable as a boost converter, a buck converter or a buck-boost converter.

According to a second aspect, the invention provides an electrical power distribution system for a host vehicle comprising a power converter according to the first aspect.

According to a third aspect, the invention provides vehicle comprising an electrical power distribution system according to the second aspect.

DETAILED DESCRIPTION

Referring first toFIG.1, a host vehicle is shown generally at100. In the example the host vehicle is a semi-truck comprising a tractor unit110and a trailer unit120. A transport climate control unit (CCU)130is coupled to the trailer unit120, and can be used to control environmental conditions such as temperature, humidity, air quality, or combinations thereof within the trailer unit120, so as to provide suitable environmental conditions for a load being transported in the trailer unit120. The CCU130in this example receives electrical power from the tractor unit110via one or more electrical cables140.

FIG.2is a schematic representation of an example electrical power distribution system for the tractor unit110ofFIG.1. The electrical power distribution system, shown generally at200inFIG.2, comprises, in this example, a power distribution unit (PDU)210configured to receive electrical power from a plurality of different sources, and to distribute electrical power to a plurality of loads as required.

The power distribution system200in this example thus includes a high voltage battery220, which is coupled to an input of the PDU210to supply high voltage DC (HVDC) electrical power to the PDU210, and to receive power from the PDU210to charge the battery220. The high voltage battery220may supply a DC voltage of the order of 400V, for example.

The power distribution system200further includes a generator230configured to generate high voltage AC (HVAC) electrical power, which may be, for example, three-phase AC. The generator230is coupled to a mechanical component of the tractor unit110(e.g. an axle, flywheel or the like), and is configured to convert mechanical energy from movement (e.g. rotation, displacement) of the mechanical component into the HVAC power. One or more electrical outputs of the generator230are coupled to inputs of an inverter240, which is configured to convert the HVAC output by the generator230into HVDC. The DC output of the inverter240may have a magnitude of, for example, 400V. An output of the inverter240is coupled to an input of the PDU210, so as to supply the HVDC to the PDU210.

The power distribution system200further includes a power converter250, which is operable in an AC-DC mode to convert between AC power, e.g. HVAC power from a shore/utility power source260external to the tractor unit110or from a generator (e.g. generator230or some other generator such as an alternator of a prime mover of the host vehicle), and DC power. The power converter250is coupled to a first input filter270, which can in turn be coupled to the shore/utility power source so as to supply HVAC power to the power converter250. The power converter250is also coupled to a second input/output filter280, which is in turn coupled to the PDU210, such that HVDC power can be supplied by the power converter250to the PDU210. The power converter250may supply HVDC to the PDU210at a magnitude of 700V, for example. The power converter250is also coupled to a third output filter290, which can be coupled to the CCU130to supply HVAC power to the CCU130, e.g. to power a compressor driver of the CCU130.

The power converter250may also be operable in a DC-DC mode to convert DC at a first voltage magnitude to DC at a second voltage magnitude. For example, the power converter250may be operable in a boost mode to convert a DC input voltage of relatively lower magnitude (e.g. 400V DC) to a DC voltage of relatively higher magnitude (e.g. 700V DC). Additionally or alternatively, the power converter250may be operable in a buck mode to convert a DC input voltage of relatively higher magnitude (e.g. 700V DC) to a DC output voltage of relatively lower magnitude (e.g. 400V DC). Thus, the power converter250may be operable as a boost converter, a buck converter or a buck-boost converter.

FIG.3is a schematic representation of example power conversion circuitry for a power converter that converts between AC and DC electrical power or between DC power at a first voltage magnitude and DC power at a second voltage magnitude.

The power conversion circuitry, shown generally at300inFIG.3, comprises exemplary voltage source converter circuitry which is operable in an AC-DC mode and/or in a DC-AC mode. The voltage source converter circuitry includes first, second and third half-bridge modules310,320,330, a DC link340and a DC link capacitor350.

The first half-bridge module310includes a first switching element,312, connected in series with a second switching element314. In this example the first and second switching devices are insulated gate bipolar transistors (IGBTs), but it will be appreciated by those skilled in the art that other semiconductor switching devices may also be used.

A first freewheel diode316is connected in an inverse parallel configuration with the first switching device312, with its anode connected to an emitter of the first switching device312and its cathode connected to a collector of the first switching device312.

A second freewheel diode318is connected in an inverse parallel configuration with the second switching device314, with its anode connected to an emitter of the second IGBT314and its cathode connected to a collector of the second switching device314.

The emitter of the first switching device312is connected to the collector of the second switching device314. The collector of the first switching device312is connected to positive rail342of the DC link340, which in turn is connected to a first terminal of the DC link capacitor350, whilst the emitter of the second switching device314is connected to a negative rail342of the DC link340, which in turn is connected to a second terminal of the DC link capacitor350.

A node315between the first and second switching devices312,314is coupled to a first terminal of an AC input/output block380such that a first phase382of an AC input/output can be coupled to the node315.

The gates of the first and second switching devices312,314are connected to outputs of a controller370, which is configured to generate control signals to switch the first and second switching devices312,314on and off in a predetermined sequence when the power conversion circuitry is operating in the DC-AC mode to convert from a DC input voltage at the DC link340to an AC output voltage at the AC input/output block380.

Thus, when the first switching device312is switched on (in response to an appropriate control signal from the controller370), the first phase382is coupled to the positive rail342of the DC link340. When the second switching device314is switched on (in response to an appropriate control signal from the controller370), the first phase382is coupled to the negative rail344of the DC link340. It will be appreciated that the first and second switching devices should not be switched on at the same time, as this would result in a short circuit between the positive and negative rails342,344of the DC link340. Thus the controller370is configured to control the timing of control signals to the first and second switching devices312,314to ensure complementary operation of the first and second switching devices312,314(i.e. when the first switching device312is switched on the second switching device314is switched off, and vice-versa).

The second half-bridge module320is of a similar construction as the first half-bridge module310, and comprises first and second switching devices322,324(which in this example are IGBTs) and first and second freewheel diodes326,328, which are connected in the same manner as the first and second switching devices312,314and the first and second freewheel diodes316,318of the first half-bridge module310. A node325between the first and second switching devices322,324is coupled to a second terminal of the AC input/output block380such that a second phase384of an AC input/output can be coupled to the node325.

The gates of the first and second switching devices322,324are connected to outputs of the controller370, which is configured to generate control signals to switch the first and second switching devices322,324on and off in a predetermined sequence when the power conversion circuitry operating in the DC-AC mode to convert from a DC input voltage to an AC output, as described above.

The third half-bridge module330is of a similar construction as the first and second half-bridge modules310,320, and comprises first and second switching devices332,334(which in this example are IGBTs) and first and second freewheel diodes336,338, which are connected in the same manner as the first and second switching devices312,314and the first and second freewheel diodes316,318of the first half-bridge module310. A node335between the first and second switching devices332,334is coupled to a third terminal of the AC input/output block380such that a second phase386of an AC/DC input/output can be coupled to the node335.

The gates of the first and second switching devices332,334are connected to outputs of the controller370, which is configured to generate control signals to switch the first and second switching devices332,334on and off in a predetermined sequence when the power conversion circuitry is operating in the DC-AC mode to convert from a DC input voltage to an AC output, as described above.

Thus the power conversion circuitry300is operable in a DC-AC mode to convert DC electrical power received at the DC link340into three-phase AC power at the AC input/output block380, using appropriate timing or phasing of control signals to the IGBTs312-334.

The power conversion circuitry300is also operable in an AC-DC mode to convert three-phase AC electrical power received at the AC input/output block380into DC electrical power at the DC link340. The first phase382is coupled to the node315, the second phase384is coupled to the node325and the third phase386is coupled to the node335.

Diodes316,318,326,328form a full bridge rectifier between the first and second phases382,384. Similarly, diodes326,328,336,338form a full bridge rectifier between the second and third phases, and diodes336,338,316,318form a full bridge rectifier between the third and first phases. As the three phases of the input AC rotate, one of the diodes316,326,336conducts current to the positive rail342of the DC link340, and one of the diodes318,328,338conducts current to the negative rail344of the DC link340. Which of the diodes316-336conducts at a given time is governed by the positive voltages at the anodes of each of the diodes316-336; the diode with the most positive (i.e. highest magnitude) anode voltage at a given time will conduct. Similarly, which of the diodes318-338conducts at a given time is governed by the negative voltages at the cathodes of each of the diodes318-338; the diode with the most negative (i.e. highest magnitude) voltage at its cathode at a given time will conduct.

One problem with power conversion circuitry of the kind shown inFIG.3is that it provides an uncontrolled current path from an external AC source or DC source to the DC link340, via the diodes316-338. Thus, when a voltage is applied to the conversion circuitry300via the AC input/output block380, the voltage at the DC link340will rise immediately, and this can lead to current peaks or spikes, which can destroy or damage the diodes316-338.

To prevent damage to the diodes316-338from such overcurrent conditions, the DC link capacitor350may be pre-charged before the external AC source is coupled to the power conversion circuitry, to raise the voltage at the DC link340to a level equal to (or at least close to) or greater than the peak voltage of the external AC source or DC source. Pre-charging the DC link capacitor350to a voltage equal to or greater than the peak voltage of the external AC source in this way prevents any immediate flow of current from the external AC source through the diodes316-338, thus preventing damage to the diodes.

Examples of circuitry for pre-charging the DC link capacitor350will now be described with reference toFIGS.4-7.

FIG.4is a schematic representation of power conversion circuitry for a power converter, in which a voltage source external to the power converter is used for pre-charging a DC link capacitor. The power conversion circuitry, shown generally at400inFIG.4, includes a number of elements in common with the power conversion circuitry300ofFIG.3, and so common reference numerals have been used to denote such common elements, which will not be described again here for the sake of clarity and brevity.

The power conversion circuitry400differs from the power conversion circuitry300in that it includes pre-charge circuitry410coupled to the AC/DC input/output block380and configured to receive AC power from an external AC source.

The pre-charge circuitry410includes a main switch412(e.g. a contactor) which, when closed, couples the input/output block380to the external AC/DC source, and a series combination of a pre-charge switch414(e.g. a contactor) and a resistor416, coupled in parallel with the main AC switch.

To pre-charge the DC link capacitor350, the main AC switch412is opened and the pre-charge switch414is closed (e.g. in response to appropriate control signals from the controller370). Current thus flows from the external AC source through the resistor416and through the diodes316-338to the DC link capacitor350to charge the DC link capacitor350. The resistor416limits the inrush current that flows when the pre-charge switch is closed to a level that will not damage the diodes316-338. When the DC link capacitor350has been charged to a level at which the DC link voltage is equal or close to the peak voltage of the external AC source, the pre-charge switch414can be opened and the main AC switch412can be closed (e.g. in response to appropriate control signals from the controller370). Because the DC link capacitor350has been pre-charged, there is no immediate flow of current from the external AC source through the diodes316-338, thus preventing damage to the diodes.

The pre-charge circuitry410is thus effective in preventing damage to the diodes316-338. However, the switches412,414and resistor416can be undesirably heavy and expensive. Additionally, if there are multiple different external AC/DC sources, separate pre-charge circuitry410must be provided for each external AC/DC source, which further increases weight and cost.

FIG.5is a schematic representation of alternative power conversion circuitry for a power converter, in which a flyback converter internal to the power converter is used for pre-charging a DC link capacitor.

The power conversion circuitry, shown generally at500inFIG.5, includes a number of elements in common with the power conversion circuitry300ofFIG.3, and so common reference numerals have been used to denote such common elements, which will not be described again here for the sake of clarity and brevity.

The power conversion circuitry500differs from the power conversion circuitry300in that it includes pre-charge circuitry510coupled to the DC link340. The pre-charge circuitry510in this example comprises a flyback converter comprising a transformer520, a switching device530, a diode540and a pre-charge switch550. In this example the switching device530is a field effect transistor (FET), but it will be appreciated by those skilled in the art that an alternative semiconductor switching device may also be used.

A first terminal of a primary coil522of the transformer520is coupled to the pre-charge switch550. A second terminal of the primary coil522is coupled to a drain terminal of the switching device530. A source terminal of the FET530is coupled to the negative rail344of the DC link340.

A first terminal of a secondary coil524of the transformer520is coupled to the negative rail344of the DC link340. A second terminal of the secondary coil524is coupled to an anode of the diode540. A cathode of the diode540is coupled to the positive rail342of the DC link340.

In operation of the pre-charge circuitry510to pre-charge the DC link capacitor350prior to coupling the AC/DC input/output block380to an external voltage source, the pre-charge switch550is closed (e.g. in response to an appropriate control signal from the controller370). This has the effect of coupling the primary coil522of the transformer520to a low-voltage DC power supply560, which may be, for example a DC power supply which provides a supply voltage (e.g. 15V DC) to the controller370. A control signal is supplied, e.g. by the controller370, to a gate terminal of the switching device530to alternately switch the switching device530on and off.

When the switching device530is switched on, an increasing current flows through the primary coil522, causing a magnetic field to develop in the transformer520. The diode540is reverse biased, so no current can flow from the DC link capacitor to a secondary coil524of the transformer520.

When the switching device530is switched off, the primary coil522is decoupled from the power supply560. Thus current stops flowing in the primary coil522, which causes the magnetic field to collapse, inducing a current in the secondary coil524, which flows through the diode540to the DC link capacitor350, thereby charging the DC link capacitor350.

Over a plurality of on-off cycles of the switching device530the DC link capacitor350is charged such that a voltage at the DC link340is equal to or greater than the peak voltage of the external voltage source. Once this voltage is reached, the pre-charge switch550can be opened (e.g. in response to an appropriate control signal from the controller370) and the AC/DC input/output block380can be coupled to the external voltage source without risk of damage to the diodes316-338from an overcurrent condition.

In an alternative implementation the pre-charge switch550may be omitted, because the diode540provides decoupling between the DC power supply560and the positive rail342of the DC link340, so the pre-charge switch is not required to prevent current flow from the DC power supply560and the positive rail342.

The pre-charge circuitry510is thus effective in preventing damage to the diodes316-338, and, in contrast to the pre-charge circuitry410ofFIG.4, the same pre-charge circuitry510can be used for every external voltage source (because the pre-charge circuitry is internal to the power converter). However, the transformer520is typically heavy and expensive, and thus the pre-charge circuitry510may undesirably add to the cost and weight of the power conversion circuitry500.

FIG.6is a schematic representation of further alternative power conversion circuitry for a power converter, in which a boost converter internal to the power converter is used for pre-charging a DC link capacitor.

The power conversion circuitry, shown generally at600inFIG.6, includes a number of elements in common with the power conversion circuitry300ofFIG.3, and so common reference numerals have been used to denote such common elements, which will not be described again here for the sake of clarity and brevity.

The power conversion circuitry600differs from the power conversion circuitry300in that it includes pre-charge circuitry610coupled to the DC link340. The pre-charge circuitry610comprises a boost converter comprising an inductor620, a switching device (in this example a field effect transistor (FET))630, a diode640and a pre-charge switch650.

A first terminal of the inductor620is coupled to the pre-charge switch650. A second terminal of inductor620is coupled to a node612between a drain terminal of the FET630and an anode of the diode640. A source terminal of the FET630is coupled to the negative rail344of the DC link340. A cathode of the diode640is coupled to the positive rail342of the DC link340.

In operation of the pre-charge circuitry610to pre-charge the DC link capacitor350prior to coupling the AC input/output block380to an external AC voltage source, the pre-charge switch650is closed (e.g. in response to an appropriate control signal from the controller370). This has the effect of coupling the first terminal of the inductor620to a low-voltage DC power supply560, which may be, for example a DC power supply which provides a supply voltage (e.g. 15V DC) to the controller370. A control voltage is supplied, e.g. by the controller370, to a gate terminal of the switching device630to alternately switch the switching device630on and off.

When the switching device630is switched on, an increasing current flows through the inductor620, causing a magnetic field to develop around the inductor620. The diode640is reverse biased, so no current can flow from the DC link capacitor to the inductor620.

When the switching device630is switched off, the inductor620is decoupled from the power supply560. The magnetic field collapses, inducing a current in the inductor620, which flows through the diode640to the DC link capacitor350, thereby charging the DC link capacitor350.

Over a plurality of on-off cycles of the switching device630the DC link capacitor350is charged such that a voltage at the DC link340is equal to or greater than the peak voltage of the external voltage source. Once this voltage is reached, the pre-charge switch650can be opened (e.g. in response to an appropriate control signal from the controller370) and the input/output block380can be coupled to the external voltage source without risk of damage to the diodes316-338from an overcurrent condition.

The pre-charge circuitry610is thus effective in preventing damage to the diodes316-338, and, in contrast to the pre-charge circuitry410ofFIG.4, the same pre-charge circuitry610can be used for every external voltage source (because the pre-charge circuitry is internal to the power converter). However, the pre-charge circuitry610requires a dedicated inductor620, which again adds to the cost of the power converter.

FIG.7is a schematic representation of power conversion circuitry for the power converter250of the electrical power distribution system ofFIG.2, in which a boost converter that uses an inductive component of a host vehicle or the CCU130is used for pre-charging a DC link capacitor.

The power conversion circuitry, shown generally at700inFIG.7, includes a number of elements in common with the power conversion circuitry600ofFIG.6, and so common reference numerals have been used to denote such common elements, which will not be described again here for the sake of clarity and brevity.

Like the power conversion circuitry600, the power conversion circuitry700includes pre-charge circuitry710comprising a boost converter. However, the power conversion circuitry700differs from the power conversion circuitry600in that, instead of a dedicated inductor620, the inductance of an external inductive component720, e.g. an inductive component of the of the host vehicle (e.g. tractor unit110) or the CCU130acts as an inductor for the boost converter. For example, the inductance of a stator winding of a motor (e.g. a fan motor) or a generator of the host vehicle or the CCU may act as the inductor for the boost converter of the power conversion circuitry700.

Thus in the pre-charge circuitry710the pre-charge switch650is coupled to a first inductor coupling terminal722, and the node612between the drain terminal of the switching device630and an anode of the diode640is coupled to a second inductor coupling terminal724. The first and second inductor coupling terminals722,724are configured to be coupled to first and second terminals of a suitable external inductance, e.g. an inductive component of the host vehicle or the CCU130. As indicated above, a stator winding of a motor720, e.g. a fan motor, or a generator of the host vehicle or the CCU130is one example of a suitable external inductance.

For the avoidance of doubt, although the external inductive component720is shown within the boundary of the pre-charge circuitry710inFIG.7, it is to be appreciated that the external inductive component720is not necessarily co-located with the pre-charge circuitry710, but may instead be provided in some other location and coupled to the first and second inductor coupling nodes722,724by wires or other suitable conductors.

As in the pre-charge circuitry610, a source terminal of the switching device630of the pre-charge circuitry710is coupled to the negative rail344of the DC link340. A cathode of the diode640is coupled to the positive rail342of the DC link340.

The pre-charge circuitry710operates in the same manner as the pre-charge circuitry610to pre-charge the DC link capacitor350to a voltage equal to or greater than a peak voltage of an external voltage source to which the power conversion circuitry700is to be coupled, by alternately switching the switching device630on and off (using control signals provided to its gate terminal, e.g. by the controller370), to provide a charging current to the DC link capacitor350until a desired DC link voltage is reached, at which point the pre-charge switch can be opened and the external voltage source can be coupled to the power conversion circuitry700.

The pre-charge circuitry710is thus effective in preventing damage to the diodes316-338, and, in contrast to the pre-charge circuitry410ofFIG.4, the same pre-charge circuitry710can be used for every external voltage source (because the pre-charge circuitry is internal to the power converter). Moreover, the pre-charge circuitry710does not require a dedicated inductor, which reduces the cost and weight of the power converter circuitry700, and the space required to accommodate it (as compared to the power converter circuitry400,500,600ofFIGS.4-6), as well as improving reliability, in the sense that there are fewer components that could malfunction.

Thus the pre-charge circuitry710contributes to an improved power converter250with reduced cost, weight and space requirements, as well as improved reliability.

InFIG.7the switching device630and diode640of the boost converter are shown as dedicated components of the pre-charge circuitry710. As will be appreciated by those skilled in the art, a motor of the host vehicle or the CCU130may have an associated power converter (provided in the host vehicle or the CCU130) which supplies one or more appropriate supply voltages to the motor. By re-using existing components of this power converter, the number of components required to implement pre-charge circuitry for pre-charging the DC link capacitor350can be reduced further.

FIG.8is a schematic representation of power conversion circuitry for the power converter250of the electrical power distribution system ofFIG.2, in which the boost converter for pre-charging the DC link capacitor350is constituted from a motor of a host vehicle or the CCU130and elements of a power converter that provides supply voltages to the motor.

The power conversion circuitry, shown generally at800inFIG.8, includes a number of elements in common with the power conversion circuitry600ofFIG.6, and so common reference numerals have been used to denote such common elements, which will not be described again here for the sake of clarity and brevity.

In the power conversion circuitry800ofFIG.8, elements of a power converter810that is used to provide supply voltages to a motor820are re-used as part of a boost converter for pre-charging the DC link capacitor350. This re-purposing of the elements of the power converter810is possible because during pre-charging of the DC link capacitor350the motor820is not in use.

The power converter810in this example is generally similar to the power conversion circuitry300ofFIG.3. The power converter810thus includes first, second and third half-bridge modules830,840,850, each comprising first and second switching devices and associated first and second inverse parallel connected freewheel diodes. Elements of the power converter810that are not re-used as part of the boost converter for pre-charging the DC link capacitor350are shown in chain-dashed outline inFIG.8.

The inductance of the boost converter used to pre-charge the DC link capacitor350is provided by a stator coil of the motor820. The switching device630of the boost converter is provided by the second switching device844of the second half-bridge module840of the power converter810, and the diode640of the boost converter is provided by the first freewheel diode846of the second half-bridge module850of the power converter810.

Thus the boost converter used to pre-charge the DC link capacitor350in the power conversion circuitry800ofFIG.8comprises the pre-charge switch650, a stator coil of the motor820, the switching device844and the freewheel diode846, and this boost converter is operable in the manner described above with reference toFIGS.6and7to pre-charge the DC link capacitor350from the low-voltage DC power supply560.

By re-using the existing elements of the converter810in this way, the number of additional components required to implement pre-charge circuitry for pre-charging the DC link capacitor350can be minimised, thus reducing the physical size, weight and cost of the pre-charge circuitry, as well as improving reliability, because of the reduced number of components that could malfunction.

In the examples described above with reference toFIGS.3-8, the power conversion circuitry comprises two-level voltage source converter circuitry, but it will be appreciated by those skilled in the art that the power conversion circuitry could instead comprise a voltage source converter of another topology, e.g. a three-level converter (e.g. with a floating capacitor) or a modular multi-level converter, and that the approaches to pre-charging the DC link capacitor described above are equally applicable to any such power conversion circuitry. More generally, the described approaches are suitable for pre-charging the DC link capacitor of any voltage source inverter or converter with an implicit diode rectifier.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality. Any reference signs in the claims shall not be construed so as to limit their scope.