Voltage source converter and method for operation of a voltage source converter

Abstract

A voltage source converter has a half bridge (18) and an arrangement having two current valves (19, 20) connected in series, the arrangement being configured to perform voltage measurements for determining the value of a DC voltage between opposite poles (21, 22) on the DC side of the converter. Each current valve comprises a semiconductor device (23, 24) controlled by an associated gate drive member (29, 30), the gate drive members (29, 30) each forming a gate drive component of a gate drive unit (28) common to the two current valves. The gate drive unit (28) comprises an isolated bidirectional communication link (33) between the gate drive members. The arrangement is included in the gate drive unit and is configured to measure the entire DC voltage between the opposite poles (21, 22). A converter control device (31) calculates a control signal based on the result of the voltage measurement and sends the control signal to the gate drive unit.

Description

Technical Field

[0001] The present invention relates to a voltage source converter, the voltage source converter comprising:

[0002] a half-bridge having two current valves connected in series and configured to be connected to opposite poles of a DC source / load, each of said current valves comprising a semiconductor device of the turn-off type and a rectifying diode connected in anti-parallel with the semiconductor device, the midpoint between the two current valves of the half-bridge forming the AC side of the converter and configured to be connected to an AC load / source,

[0003] two gate drive components, each gate drive component comprising a logic device and a gate drive stage, configured to control the semiconductor device of the current valve to be turned on and off according to a control signal from the converter control device,

[0004] the converter control device is configured to send control signals to the gate drive means for controlling the operation of the converter according to a pulse width modulation mode for generating an AC fundamental voltage and current on the AC side, and

[0005] • an arrangement configured to perform a voltage measurement for providing a value of a DC voltage between said opposing poles to a first said logic device, the first said logic device being configured to send information about said DC voltage value to a converter control device.

[0006] The invention is not limited to any specific use of such a converter, but in some parts of this disclosure its use in a rail vehicle such as a railway vehicle will be explained for the purpose of illustrating the invention without thereby limiting the invention to this application.

[0007] Such converters are used to convert a direct voltage into an alternating voltage or vice versa for different purposes. Thus, in the case of a motor converter, the AC side is considered to be the load and the DC side the source, or vice versa in the case of a line converter. The invention is not limited to any number of phases of the voltage applied to the AC side, although three-phase voltage is the most common, nor is the invention limited to any particular level of such voltage or electrical power to be fed through the converter. Thus, in the case of a three-phase voltage, the converter has at least three of the said half-bridges between the relative poles of the DC side (in order to allow high currents, each phase can theoretically have a plurality of half-bridge modules connected in parallel).

[0008] The semiconductor device of the current valve may be any semiconductor device of a turn-off type, such as an IGBT or a MOSFET.

[0009] The control of a converter of the type defined in the introduction, in particular when used for high power applications, such as supplying electric energy to drive motors of railway vehicles, generally requires information about the level of the DC voltage on the DC side of the converter. One reason for this is that the semiconductor devices of the current valve must be prevented from being subjected to excessively high voltages. To this end, the value of the DC voltage determined by the arrangement can be used for the control of a chopper, by means of which the level of the DC voltage can be controlled. The exact value of the DC voltage can also be used as an input to the control of the gate drive means when trying to optimize the switching of the current valve.

[0010] The converter control device, for the sake of simplicity and in order to avoid expensive high voltage insulation of its power supply and its communication ports to ground potential, i.e. to most of the communication ports of the vehicle body, while the converter main circuit can be negatively grounded, i.e. connected with its negative DC voltage pole via a return conductor to the running rail, or mid-point grounded, i.e. with a high impedance voltage divider connected between its positive and negative poles, wherein the midpoint of the voltage divider is connected to ground, i.e. to the vehicle body. In the latter case, an electrically isolated communication channel between the converter control device and the gate drive unit is obviously necessary, and in the case of negatively grounded, this is also preferred in order to avoid electromagnetic interference and to enable dielectric testing of the main circuit without temporarily disconnecting the communication link. Background Art

[0011] It is known to use separate voltage measuring devices, such as closed-loop voltage sensors, as an arrangement for performing voltage measurements for determining the value of the DC voltage between the opposite poles in a voltage source converter of the type defined in the introduction. However, the cost and effort of producing and installing such measuring devices are high and separate power supplies are required. Furthermore, redundant measuring devices may then also be required in order to ensure the operation of the converter.

[0012] In order to solve these problems, it is proposed in WO 2007 / 059985 to use an existing voltage measuring device integrated in a valve control unit to provide the converter control device with information about the DC voltage across the corresponding current valve. In this method, the voltage across the current valve is then measured with the semiconductor device switched off to obtain the value of the DC voltage. Although this known converter concept works well, there are of course ongoing attempts to improve the performance of such converters. Summary of the invention

[0013] It is an object of the invention to provide a voltage source converter and a method for the operation of such a voltage source converter of the type defined in the introduction which are improved in at least some respects with respect to known such converters and methods.

[0014] This object is obtained with respect to a converter by providing such a converter with the features listed in the characterizing part of the appended patent claim 1 .

[0015] Thus, the two gate drive members form the gate drive part of a common gate drive unit for the two current valves, and this gate drive unit contains an electrically isolated bidirectional communication link interconnecting the gate drive members. An arrangement is included in the gate drive unit and comprises a voltage divider connected across the two current valves so as to measure the overall DC voltage between opposite poles, and the converter control device is configured to calculate a control signal based on the results of the measurement performed by the arrangement and send the control signal to the gate drive unit.

[0016] One advantage of the converter according to the invention is that by including the gate drive members for both current valves in one gate drive unit and providing an isolated bidirectional communication link between the gate drive members, the converter control device can control the entire phase, i.e. both current valves, by a single control signal telling the entire phase what to do, e.g. switch on either current valve or switch off both current valves. By means of the communication link between the two gate drive members, the two gate drive members will now have the possibility of direct interaction, which is not the case for known such configurations of the phases where the two gate drive members are separated.

[0017] Furthermore, having a voltage divider common to both gate drive members results in a simpler design, which gives a reduced number of components and economic advantages over known converters of this type. And by having an arrangement for measuring the overall DC voltage included in the gate drive unit, the use of a voltage sensor in the DC link connecting the converter to a DC source / load can be omitted.

[0018] According to an embodiment of the invention, the voltage divider has an output having one of the poles as reference potential and the output is connected to a processing component comprised in one of the gate drive members, a first gate drive member. This helps to obtain a lower number of components in combination with a high-speed communication link to the converter control device, which is common to the entire gate drive unit.

[0019] According to another embodiment of the invention, the first gate drive member is configured to also send information about the measured DC voltage directly to the second gate drive member, and the two gate drive members are configured to use the information about this voltage to optimize the switching of the semiconductor device of the corresponding current valve. By the presence of a communication link between the gate drive members, the switching of the semiconductor device of the current valve can be optimized in this way.

[0020] According to another embodiment of the invention, the first gate drive means is configured to use the value of the DC voltage measured by the arrangement directly for control of the semiconductor device. This is a preferred way to achieve the results obtainable by the aforementioned embodiments.

[0021] According to another embodiment of the present invention, a voltage source converter comprises three said half bridges, each of said half bridges having said gate drive unit, said gate drive unit having two said gate drive members for generating a three-phase AC fundamental voltage and current on said AC side. This is a converter of the type used to supply electric energy to the driving motor of a railway vehicle and then also to send electric energy from the motor constituting the motor when the vehicle is braked, and these machines act as generators to the DC side of the converter.

[0022] According to another embodiment of the present invention, the converter comprises an even number of said half bridges, each of said half bridges having said gate drive unit, said gate drive unit having two said gate drive members, wherein each pair of half bridges is configured to be connected to one secondary winding of an AC line railway vehicle main transformer and to generate a single-phase AC fundamental voltage and current therebetween on said AC side. Thus, this converter is configured to be used as a line converter.

[0023] According to another embodiment of the invention, said arrangement is comprised in a gate drive unit for each said phase.Since several gate drive units will thereby provide a measurement of the same DC voltage, the redundancy / fault tolerance of the system is increased.

[0024] According to another embodiment of the present invention, the semiconductor device of the current valve is an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

[0025] According to another embodiment of the invention, the converter is a rail vehicle converter, which is configured to be arranged on a rail vehicle and is, for example, a motor converter configured to deliver power to an electric motor for driving the vehicle via said AC side of the converter, or an auxiliary converter configured to deliver voltage on said AC side of the converter for a heating / cooling system of the vehicle and for electrical devices, such as via sockets arranged in said vehicle. This is a preferred application of this type of voltage source converter.

[0026] This object with respect to a method is achieved by providing a method according to the attached independent method claim, and the advantages of such a method and possible embodiments thereof, such as defined in the dependent method claims, appear clearly from the above discussion of the Voltage Source Converter according to the invention.

[0027] The invention also relates to a computer program, a computer program product, an electronic converter control unit and a rail vehicle according to the appended claims to which it relates.

[0028] Other advantages and advantageous features of the present invention will become apparent from the following description of embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] With reference to the accompanying drawings, the following is a detailed description of an embodiment of the present invention cited as an example. In the drawings:

[0030] Figure 1 is a very schematic view illustrating how different types of converters of the type to which the invention relates can be arranged and controlled in a rail vehicle,

[0031] Figure 2 is a schematic circuit diagram of a converter half-bridge according to an embodiment of the present invention, and

[0032] Figure 3 is a schematic diagram illustrating an electronic converter control unit for implementing the present invention. DETAILED DESCRIPTION

[0033] Since the invention is particularly suitable for use in rail vehicles, without limiting the invention to this field of use, reference will now be made to Figure 1 Some possible ways of using a voltage source converter according to the invention are briefly described. Figure 1 Schematically illustrates how power can be fed from an AC power line 2 to a rail vehicle 1 and used in the vehicle. The vehicle is configured to move along an AC power line 2, which acts accordingly as an AC source and which can carry, for example, a single-phase AC voltage of 15 kV and 16 2 / 3 Hz (Sweden, Germany, etc.) or a single-phase AC voltage of 25 kV and 50 Hz (Denmark, China, India, etc.). The vehicle has a transformer 3 for converting the voltage from the power line 2 to a suitable level. Here the transformer has two secondary windings 4, 5, one of which is connected to a line converter 6, which is used to deliver a DC voltage of, for example, 0.8-3 kV at its output. This DC voltage is delivered to an auxiliary converter 7, which is controlled by a converter control device 8 for generating a series of pulses according to a pulse width modulation mode for delivering a three-phase AC voltage at the output of the auxiliary converter 7. The output of this converter is connected to a three-phase transformer 9 and to a harmonic filter 10 for smoothing the AC voltage delivered by the distribution network 11 to sockets arranged in the rail vehicle, such as for the connection of computers, and to lighting, heating and other electrical appliances.

[0034] The other secondary winding 4 of the transformer is connected to a line converter 12, which is configured to deliver a DC voltage on its output to the input of a voltage source converter in the form of a motor converter 13, which is used to deliver a three-phase AC voltage on its output to an electric motor 15 in the form of an electrical machine for driving the vehicle. Each converter 12, 13 is controlled by a converter control device 16, 14, which determines the PWM mode of the converter. The motor converter control device 14 will receive commands from the driver of the vehicle for adapting the frequency (induction motor) or phase angle (permanent magnet motor) of the fundamental voltage delivered to the stator winding of the electric motor to the commanded traction effort / traction force. In the event of braking, the vehicle power will flow in the direction from the electric motor to the AC power supply line through the line converter 12, which is controlled to deliver a single-phase AC voltage on its AC side. The converters 6, 7, 12 and 13 can be voltage source converters according to the present invention. It is to be noted that Figure 1 The electrical system shown in FIG. 1 is only one representation of several possible representations of an electrical system in a rail vehicle.

[0035] exist Figure 2 Schematically illustrated in FIG is a single phase of a voltage source converter 17 according to an embodiment of the invention. The voltage source converter has a half-bridge module 18 with two current valves 19, 20 for each phase, which are connected in series and are configured to be connected to opposite poles 21, 22 of a DC source or load, such as connected to Figure 1 1 and 13. Each current valve has a semiconductor device 23, 24 of the turn-off type in the form of a MOSFET (IGBT is also possible) and a rectifier diode 25, 26 connected in anti-parallel with the semiconductor device 23, 24. In this case of an AC load, the midpoint between the two current valves of the half bridge forms the AC side 27 of the converter and is configured to be connected to an inductive impedance.

[0036] The voltage source converter has a gate drive unit 28 for each phase, which has a first gate drive component 29 configured to control the MOSFET 24 of the first current valve 20 to be turned on and off (typically at a switching frequency of several kHz) and a second gate drive component 30 configured to control the MOSFET 23 of another, second current valve 19 to be turned on and off (typically at a switching frequency of several kHz), for generating an AC voltage and current on the AC side 27.

[0037] The converter control device 31 common to the three-phase gate drive units is configured to send control signals to each phase to the gate drive unit 28 through a high-speed isolated bidirectional communication link 32 for controlling the operation of the converter, in which the control signal is first received by the first gate drive component 29, which processes the signal into separate ON / OFF control signals for the first gate drive component 29 itself and the ON / OFF control signal for the second gate drive component 30 through a logic device 46, and sends the ON / OFF control signal for the second gate drive component 30 to the logic device 47 of the interconnected gate drive components through an isolated bidirectional communication link 33, so that the gate drive stages 34, 35 turn on or off the corresponding MOSFETs 24, 23 to generate the desired PWM.

[0038] For the operation of the converter, it is important to know the value of the DC voltage between the poles 21, 22 on its DC side, and in order to ensure that this voltage will never reach a level that is unfavorable to the power semiconductor device (MOSFET) of the current valve, this value must be determined. For this purpose, the voltage source converter does have an arrangement configured to perform voltage measurement for determining the value of the DC voltage, and this arrangement is included in the gate drive unit 28 and includes a voltage divider 36 connected across two current valves to measure the entire DC voltage between the relative poles 21, 22 of the DC link. Such a fixed resistor divider conveys a low-voltage measurement signal that can be further processed. The same voltage divider hardware can be used for power semiconductor devices, such as IGBTs, for different voltages, such as rated 1.7kV and 3.3kV. The voltage measurement arrangement includes a resistor divider 36 and processing components 37, 38, 39, 45. The processing component is included in the first gate drive component 29, and includes a component 37, a low-pass filter 38, an analog-to-digital converter 39, and a digital low-pass filter 45 for selecting the final voltage division factor of the arrangement. The voltage division factor is controlled by the logic device 46. Impedance matching to the logic device 46 is provided by the low pass filter 38. Information about the resulting DC voltage value is sent to the converter control device 31 via the high speed communication link 32, at an update speed in the order of 10 μs, together with other phase state information. The converter control device is configured to calculate control signals based on the results of the measurements thus performed by the DC voltage measurement arrangement and to send the control signals to the gate drive unit 28.

[0039] Information about the DC voltage measured by the arrangement can be used by the converter control device together with the load current measured by a separate current sensor (not shown) to calculate the on / off time of the semiconductor device of the current valve. The gate drive unit in the voltage converter according to the present invention can autonomously use the DC voltage value information for optimizing the switching of the power semiconductor device, in particular for the switching on in the case of an IGBT. Then, the first gate drive member 29 including the arrangement will directly use the voltage value measured by the arrangement, while the other gate drive member 30 uses the value sent from the first gate drive member 29 via the communication link 33.

[0040] Advantageously, the computer program code for implementing the method according to the invention is included in a computer program which can be read into an internal memory of a computer, for example an internal memory of an electronic converter control unit of a rail vehicle. Advantageously, such a computer program is provided as a computer program product comprising a data storage medium which can be read by a computer and on which the computer program is stored. Figure 3 An electronic converter control unit 40 is illustrated very schematically and comprises execution means 41, for example a central processing unit (CPU) for executing computer software. The execution means 41 communicates with a memory 42, for example of RAM type, via a data bus 43. The electronic converter control unit 40 further comprises a non-transitory data storage medium 44, for example in the form of a flash memory or a memory of the ROM, PROM, EPROM or EEPROM type. The execution means 41 communicates with the data storage medium 44 via the data bus 43. The computer program comprises computer program code for implementing the method according to the invention.

[0041] Of course, the invention is in no way limited to the embodiments described above, since many possibilities for modifications thereof may well be apparent to a person skilled in the art without necessarily departing from the scope of the invention as defined in the appending claims.

[0042] For redundancy it is advantageous to have a voltage measuring arrangement in each gate drive unit of a multiphase voltage source converter, but in case of a three phase voltage source converter it is also within the scope of the invention to have an arrangement in only one or two of the gate drive units.

[0043] Furthermore, one gate drive unit may control multiple half-bridge semiconductor modules connected in parallel but belonging to the same phase, for example four modules connected in parallel and each module having two current valves connected in series, forming a total of 8 current valves for the phase.

Claims

1. A voltage source converter for providing electric energy to a drive motor of a rail vehicle, the voltage source converter comprising: a half-bridge (18) having two current valves (19, 20) connected in series and configured to be connected to opposite poles (21, 22) of a DC source / load, each of said current valves comprising a semiconductor device (23, 24) of the turn-off type and a rectifier diode (25, 26) connected in antiparallel to the semiconductor device (23, 24), the midpoint of the half-bridge between said two current valves forming the AC side (27) of the converter and configured to be connected to the AC load / source, two gate drive members (29, 30), each gate drive member (29, 30) comprising a gate drive stage (34, 35) and a logic device (46, 47) configured to control the semiconductor devices (23, 24) of the current valves (19, 20) to be turned on and off respectively according to a control signal from a converter control device (31), the converter control device (31) being configured to send control signals to the gate drive means (29, 30) for controlling the operation of the converter according to a pulse width modulation mode for generating an AC fundamental voltage and current on the AC side, and an arrangement configured to perform voltage measurements for providing the value of the DC voltage between the opposite poles (21, 22) to a first said logic device, the first logic device being configured to send information about the DC voltage value to the converter control device (31), characterised in that the two gate drive members (29, 30) form gate drive parts of a gate drive unit (28) common to the two current valves (19, 20), the gate drive unit comprising an electrically isolated bidirectional communication link (33) interconnecting the gate drive members, the arrangement being comprised in the gate drive unit (28), and the arrangement comprising a voltage divider (36) connected across the two current valves (19, 20) in order to measure the overall DC voltage between the opposite poles (21, 22), and the converter control device (31) being configured to calculate the control signal based on the result of the measurement performed by the arrangement and to send the control signal to the gate drive unit (28), the first gate drive means (29) being configured to also send information about the measured DC voltage directly to the second gate drive means (30), and both gate drive means being configured to use information about this voltage to optimize the switching of the semiconductor devices (23, 24) of the respective current valves (19, 20) to ensure that this voltage will never reach a level that is detrimental to the power semiconductor devices (23, 24) of the current valves, the voltage divider (36) having an output having one of the poles (21, 22) as reference potential and connected to processing means (37, 38, 39, 45) included in one of the gate drive means, a first gate drive means (29), and The first gate drive means (29) is configured to directly use the value of the DC voltage measured by the arrangement for control of the semiconductor device (24).

2. The voltage source converter according to claim 1, characterized in that: The voltage source converter comprises three half bridges (18), each half bridge (18) having a gate drive unit (28), the gate drive unit (28) having two gate drive components (29, 30) for generating a three-phase AC fundamental voltage and current on the AC side.

3. The voltage source converter according to any one of claims 1 to 2, characterized in that: The voltage source converter comprises an even number of the half bridges (18), each of the half bridges (18) having the gate drive unit (28) with two gate drive members (29, 30), wherein each pair of half bridges is configured to be connected to one secondary winding of an AC line railway vehicle main transformer, and each pair of half bridges is used to generate a single-phase AC fundamental voltage and current therebetween on the AC side.

4. The voltage source converter according to claim 2 or 3, characterized in that: The arrangement is comprised in the gate drive unit (28) for each of the phases.

5. A voltage source converter according to any one of the preceding claims, characterised in that The semiconductor device (23, 24) of the current valve is an insulated gate bipolar transistor IGBT or a metal oxide semiconductor field effect transistor MOSFET.

6. A voltage source converter according to any one of the preceding claims, characterised in that The voltage source converter is a rail vehicle converter configured to be arranged on a rail vehicle (1), and the rail vehicle converter is a motor converter (13) configured to transmit electric power to an electric motor (15) for driving the vehicle through the AC side of the converter, or the rail vehicle converter is an auxiliary converter (9) configured to transmit voltage for a heating / cooling system of the vehicle and for electrical equipment on the AC side of the converter.

7. A rail vehicle having at least one converter, the at least one converter being a converter according to any one of claims 1 to 6.

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