GB2540020A

GB2540020A - Gate drive circuit to reduce parasitic coupling

Info

Publication number: GB2540020A
Application number: GB1607876.8A
Authority: GB
Inventors: Joseph Lee Christopher; Anthony Solomon Luke; Permuy Alfred
Original assignee: GE Energy Power Conversion Technology Ltd
Current assignee: GE Energy Power Conversion Technology Ltd
Priority date: 2015-05-07
Filing date: 2016-05-05
Publication date: 2017-01-04
Anticipated expiration: 2036-05-05
Also published as: CN106130322A; CA2928189A1; GB201607876D0; CN106130322B; DE102016108187A1; US20160329889A1; US9887697B2; FR3036013B1; BR102016010404A2; FR3036013A1; GB2540020B

Abstract

A drive circuit 6, for driving a plurality of power semiconductor devices 70-1, 70-2, 70-M, includes a control module 10, a current pulse amplifier module 12 connected to the control module outputting current pulses, and a plurality of pulse receiver modules 50-1, 50-2, 50-M. A first transformer unit 20 has at least one primary transformer. The first transformer unit comprises a primary winding 22 connected to the current pulse amplifier module, and a secondary winding 24. A second transformer unit 40 has a plurality of secondary transformers, each secondary transformer comprising a primary winding 42-1, 42-2, 42-M connected to the secondary winding of the first transformer unit, and a secondary winding 44-1, 44-2, 44-M connected to a respective one of the plurality of pulse receiver modules. The first and second transformer units reduce parasitic coupling between the control module and the pulse receiver modules.

Description

GATE DRIVE CIRCUIT TO REDUCE PARASITIC COUPLING I. Field of Invention [0001] The present invention relates to an electrical system that employs a transformer based gating system for voltage isolated active power devices. II. Backgronnd of the Invention [0002] A number of different power conversion systems convert power from one form to another. For example, a multilevel power inverter is a power electronic device structured to produce alternating current (AC) waveforms from a direct current (DC) input voltage. These power conversion systems are used in a wide variety of applications, such as variable speed motor drives.

[0003] Isolation, and independent control within power conversion systems, is provided by gate drive circuitry. Gate drive circuits convert logic level control signals into appropriate voltages for switching one or more power devices within a power semiconductor group. In most cases, these circuits provide voltage isolation to prevent exposure of the logic signals to potentially dangerous high voltages on the power circuit.

[0004] Many conventional techniques provide isolation and control functionality via gate drive circuits. For example, one technique transfers a voltage directly across a barrier, via a transformer, while maintaining galvanic isolation. When using a transformer-based system, a voltage common to terminals of the secondary winding is produced when a voltage step occurs within the power semiconductor group. This common voltage causes parasitic currents to flow through the control circuit, which can cause failure or unintended operation. Another technique uses fiber optic transmission for creating the digital on-off signal, while transferring power separately with an isolated power source. These conventional techniques, however, are costly and lack precision synchronization for controlling series connected power semiconductor devices (e.g., switches). III. Summary of Embodiments of the Invention [0005] Given the aforementioned problem, a need exists for systems and methods that provide precise synchronization for controlling series connected power devices for circuits to perform in high voltage environments with a significant amount of rate of change in voltage with respect to time.

[0006] The present invention includes a drive circuit, for driving a plurality of power semiconductor devices as defined in claim 1. Optional features of the drive circuit are defined in claims 2 to 10. The first and second transformer units provide voltage isolation and reduce parasitic coupling between the control module and the pulse receiver modules by increasing common mode impedance between the two parts of the electrical system. With each additional transformer added in series between the first primary winding and last secondary winding, additional capacitance is added to the electrical system. Therefore, the collective capacitance between the first primary and the last secondary windings is decreased. The minimization of common module currents flowing through the control module is with reference to a drive circuit without the first and second transformer units or with only one transformer unit. At least one primary transformer of the first transformer unit and/or the plurality of secondary transformers of the second transformer unit may be implemented using toroids. The cores may be referenced to a voltage node within the electrical system or floating with respect to all voltage nodes within the electrical system.

[0007] The present invention further includes an electrical system as defined in claim 11. Optional features of the electrical system are defined in claims 12 to 21.

[0008] The present invention further includes a method, for driving an electrical system as defined in claim 22. An optional feature of the method is defined in claim 23. The steps of communicating the current pulses to the secondary windings of the first and second transformer units are preferably carried out without the need for amplification of the current pulses.

[0009] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. IV. Brief Description of the Drawings [0010] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.

[0011] FIG. 1 is a schematic diagram of an exemplary embodiment of an electrical system in accordance with an embodiment of the present invention.

[0012] FIG. 2 is a schematic diagram illustration of logical level signals determining four types of current pulses that can be derived in the gate drive circuit of the electrical system of FIG. 1.

[0013] FIG. 3 is a schematic diagram of illustration of an electrical system in accordance with a second embodiment of the present invention.

[0014] FIG. 4 is a schematic diagram of illustration of an electrical system in accordance with a third embodiment. V. Detailed Description of the Preferred Embodiments [0015] While the present invention is described herein with illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art with access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility.

[0016] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms “first,” “second,” and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term “or” is meant to be inclusive and mean either, any, several, or all of the listed items.

[0017] The use of “including,” “comprising,” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. The terms “circuit,” “circuitry,” and “controller” may include either a single component or a plurality of components, which are either active and/or passive components and may be optionally connected or otherwise coupled together to provide the described function.

[0018] FIG. 1 is an illustration of an exemplary electrical system 2 including a drive circuit 6 connected to a plurality of semiconductor groups 70. The drive circuit 6 includes a control module 10, a current pulse amplifier module 12, a first transformer unit 20, and a second transformer unit 40.

[0019] Control module 10 of gate drive circuit 6 includes one or more devices capable of generating logic level control signals based on particular programming. According to an embodiment, control module 10 is programmed to generate a number of logic level signals for shaping current pulses to be output to the current pulse amplifier module 12. As described below, the current pulses are used to produce the voltage signals driving power devices of each semiconductor group 70. The voltage signals are capable of turning the power devices of each semiconductor group 70 on or off using the same transformer system and without the need for additional coupled circuits.

[0020] The power devices are power semiconductor devices used as switches and capable of being selectively changed between a non-conducting (off) state and a conducting (on) state as commanded by a control input signal and can include, for example, thyristors, bipolar junction transistors (BJTs), insulated gate bipolar transistors (IGBTs), or a metal oxide semiconductor field-effect transistors (MOSFETs). The power devices can be classified into two categories with respect to drive requirements, namely non-gate oxide-isolated active power semiconductor devices and gate oxide-isolated active power semiconductor devices.

[0021] The control module 10 communicates with the current pulse amplifier module 12 by way of one or more logic signals 11. The current pulse amplifier module 12 outputs current pulses based on the logic signals 11 that are output from the control module 10.

[0022] As illustrated in FIG. 2, the logic signals 11 may include one of any number of current pulses, that transition through three logical states (e g.. High, Low, Neutral). The current pulses, for example, can include (i) a "Turn Off Pulse" that transitions each power device within each semiconductor group 70 from a conducting (on) state to a non-conducting (off) state, a (ii) a "Turn On Pulse" that transitions each power device of each semiconductor group 70 from a non-conducting state to a conducting state, and (iii) a "Refresh Off Pulse" that maintains each power device of each semiconductor group 70 in a non-conducting state when the power devices are already in an off state. Additionally, the current pulses can include (iv) a "Refresh On Pulse" that maintains each power device of each semiconductor group 70 in a conducting state when the power devices are already in an on state.

[0023] As depicted in FIG. 2, the control module 10 outputs two types of logic signals 11 (turn off, and turn on pulses) to the current pulse amplifier module 12, each representing a type of current pulse. For example, a logic signal A transitions through three logical states (e.g.. High, Low, Neutral) and another logic signal B only transitions through two logical states (e.g., High, Low).

[0024] In the electrical system 2 of FIG. 2, logic signal B produces a zero volt state across the first transformer unit 20 when logic signal A is in the neutral state. This arrangement ensures the second transformer unit 40 does not pull charge from the gates of power devices within the semiconductor groups 70 after the current pulse has been released.

[0025] As shown in FIG. 1, the current pulses based on the logic signals 11 that are provided to the current pulse amplifier module 12 are provided to the primary winding 22 of the first transformer unit 20. In response, current pulses are reflected on the secondary winding 24 of the first transformer unit 20. In other words, providing each successive current pulse to the primary winding 22 will result in a substantially identical reflected current pulse at the secondary winding 24 but scaled by the turns ratio of the transformer without the use of a current amplification module implemented in the secondary winding.

[0026] In high common mode environments, parasitic capacitive coupling between the semiconductor groups 70 and the drive circuit 6 can negatively affect the performance of the system 2, resulting in failure or unintended operation of components of the drive circuit 6. Specifically, a high rate of change in voltage with respect to time (dv/dt) of the power semiconductors causes a large voltage step to develop on primary windings (e g., primary windings 42 of the second transformer unit 40), with respect to a control voltage reference node. This voltage step results in a flow of a common mode current from the power devices within the semiconductor groups 70 towards the current pulse amplifier module 12 and the control module 10. This common mode current can interrupt typical switching of low-voltage power devices within the current pulse amplifier module 12, for example, and result in unintended operation of those low-voltage power devices. Additionally, unintended operation may lead to failure of the power devices within the semiconductor groups 70.

[0027] Additionally, common mode voltage isolation is not present within the system. Common mode voltage can cause common mode current flow through low voltage electronics and ground loops in measurement systems that have multiple grounding locations. Common mode voltage that exceeds the maximum overvoltage rating of the switches within the semiconductor groups 70 may damage components of the drive circuit 6.

[0028] The presence of the first transformer unit 20 reduces the dv/dt stresses of the control module 10 that occur when the power devices within the semiconductor groups 70 switch by increasing common mode impedance within the system 2. For example, the first transformer unit 20 lowers capacitance between the control module 10 and the power devices within the semiconductor groups 70. Including a transformer winding in series increases capacitance of the drive circuit 6 by virtue of series capacitance and thus decreases the overall capacitive coupling between the first primary winding and the last secondary winding.

[0029] In other embodiments, as illustrated in FIGs. 3 and 4, the first transformer unit 20 can include a plurality of primary transformers. In FIGs. 3 and 4 the first transformer unit 20 includes N primary transformers 21-1, 21-2, ... 21-N. Each primary transformer includes a primary winding 22-1, 22-2, ... 22-N coupled to a secondary winding 24-1, 24-2, ... 24-N.

Each of the primary windings 22-1, 22-2, ... 22-N is identical and each of the secondary windings 24-1, 24-2, ... 24-N is identical (i.e., the same magnetic core, turns ratio, and leakage inductance is employed). In FIGs. 3 and 4, the secondary winding 24-1 of the first primary transformer 21-1 is connected to the primary winding 22-2 of the second primary transformer 21-2, and so on. The primary winding 22-1 of the first primary transformer 21-1 is cormected to the current pulse amplifier module 12.

[0030] The primary windings 22-1, 22-2, ... 22-N of the primary transformers 21-1, 21-2, ... 21-N can be cormected in parallel to allocate current. In a parallel configuration, the current pluses provided by the current pulse amplifier module 12 are provided to the primary winding 22-1 of the first primary transformer 21-1 which is connected to the current pulse amplifier module 12.

[0031] Alternatively, but not shown, the primary windings of the primary transformers can he connected to one another in series so that the primary transformers have the same current. In a series configuration, the current pulses provided by the current pulse amplifier module 12 are provided to each primary winding of the primary transformers such that each primary winding will receive the same signal (i.e., the same current pulses) output from the current pulse amplifier module 12.

[0032] In some embodiments, a loop connects the primary and/or secondary winding(s) of the first transformer unit to a voltage potential within the system, and in particular to a voltage reference node, for example. By connecting each transformer winding to a voltage potential within the system, capacitive coupling is decreased as a result of the direct path back to the source of the voltage step.

[0033] The loop can connect the first transformer unit to a voltage potential located at a midpoint of multiple series voltage references of the system. In an example configuration, as illustrated in FIG. I, a loop 30 connects the secondary winding 24 of the first transformer unit 20 to a DC link 80 of the system 2, and in particular to a midpoint between two series DC link capacitors.

[0034] Specifically, the loop 30 provides additional pathways of current flow back to the source of the common mode voltage and allows the common mode current to be directed away from gating electronics (e.g., the gate circuit). The loop 30 provides a low impedance path from the semiconductor groups 70 back to the source of the reference node of the voltage step change. The connection of the drive circuit 6 to a voltage potential results in a higher parasitic impedance from the current pulse amplifier module 12 back to the loop 30 rather than through the same connection at the primary windings 42 of the second transformer unit 40, resulting in current flow along a path of least impedance that circumvents electronics within the control module 10.

[0035] Where the first transformer unit 20 includes a plurality of primary transformers 21-1, 21-2, ... 21-N, as illustrated in FIGs. 3 and 4, each of the primary transformers has an associated loop 30-1, 30-2, ... 30-N. Each loop 30-1, 30-2, ... 30-N is connected to a voltage potential of the system 2. Each loop 30 may be cormected to the same voltage potential within the system 2. For example, the loops 30-1, 30-2, ... 30-N may be connected to the midpoint of the DC link 80. In another example, illustrated in FIG. 3, the loops 30-1, 30-2, ... 30-N may be connected to one of the semiconductor groups 70 (e g., semiconductor group 70-2 as illustrated). Although not shown, a loop can also be connected to a node between two of the semiconductor groups 70.

[0036] One or more loops 30 can be connected to different voltage potentials within the system 2. For example, as illustrated in FIG. 4, the loops 30-1 and 30-N are cormected to the midpoint of the DC capacitor link 80 whilst the loop 30-2 is connected to the second semiconductor group 70-2 which will see a smaller voltage step with respect to that particular reference node.

[0037] The drive circuit 6 also includes the second transformer unit 40. The second transformer unit 40 receives current pulses from the current pulse amplifier module 12 by way of the first transformer unit 20 without the need for additional pulse amplification.

[0038] The second transformer unit 40 comprises a plurality of secondary transformers.

In particular, the second transformer unit 40 includes M primary windings 42-1, 42-2, ... 42- Μ coupled to Μ secondary windings 44-1, 44-2, ... 44-M. Each coupled primary winding and secondary winding represents a secondary transformer. Put another way, the second transformer unit 40 includes a plurality of secondary transformers with a first secondary transformer being defined by primary winding 42-1 and secondary winding 44-1, a second secondary transformer being defined by primary winding 42-2 and secondary winding 44-2, and so on to a Mth secondary transformer being defined by primary winding 42-M and secondary winding 44-M.

[0039] The primary windings 42-1, 42-2, ... 42-M are connected to the secondary winding 24 of the first transformer unit 20 (FIG. 1) or to the secondary winding 24-N of the Nth primary transformer 21-N (FIGs. 3 and 4), i.e., the last primary transformer in the series.

[0040] The primary windings 42-1, 42-2, ... 42-M of the second transformer unit 40 are connected in series so that all secondary transformers within the second transformer unit 40 will have the same signal (current pulses). That is, the current pulses received by the primary windings 42-1, 42-2, ..., 44-M of the second transformer unit 40 will result in M substantially identical reflected current pulses at the secondary windings 44-1, 44-2, ... 44-M scaled by the turns ratio of the secondary transformers.

[0041] A benefit of using the second transformer unit 40 in this manner is that it provides the M reflected current pulses at the secondary windings 44-1, 44-2, ... 44-M in a synchronized manner. This occurs while simultaneously adding capacitance in series between the control module 10 and the current pulse amplifier module 12 and the higher (potentially dangerous) voltage of semiconductor groups 70. That is, the first transformer unit 20 and the second transformer unit 40 collectively increase the common mode impedance between the control module 10 and each of the pulse receiver modules 50-1 through 50-M and decrease the total common mode current seen by the control module; the common mode current arising as a result of a semiconductor voltage step.

[0042] Each of the secondary windings 44-1, 44-2, ... 44-M of the second transformer unit 40 is connected to an associated one of Mpulse receiver modules 50-1, 50-2, ... 50-M. Each pulse receiver module 50-1, 50-2, ... 50-M is coupled to gates of the power devices of an associated one of the semiconductor groups 70. As shown in FIGs. 3 and 4, each pulse receiver module 50-1, 50-2, ... 50-M is connected to a single secondary transformer that provides current signals related to the four logic signals output by the control module 10.

[0043] Each pulse receiver module 50-1, 50-2, ... 50-M transfers and latches the received current pulses appropriate for driving the power devices of the associated semiconductor group 70 from a single secondary transformer. More specifically, each pulse receiver module 50-1, 50-2, ... 50-M performs two main functions on a received current pulse to establish a voltage (e g., gate-to-emitter voltage) to drive the power devices of the semiconductor groups 70 to either the conducting (on state) or not conducting (off state).

[0044] First, each pulse receiver module 50-1, 50-2, ... 50-M sets up and clamps to an on state gate-to-emitter voltage for a positive current pulse. Likewise, each pulse receiver module 50-1, 50-2, ... 50-M sets up and clamps to an off state gate-to-emitter voltage for a negative current pulse.

[0045] Second, each pulse receiver module 50-1, 50-2, ... 50-M remains at the on state or off state gate-to-emitter voltage after a current pulse has ended so that the power devices within an active power semiconductor group 70 can remain in either the on state or off state, respectively. In other words, the power devices are latched by the pulse receiver modules.

This prevents a flux reset action of the second transformer unit 40 from inadvertently disturbing the proper on state and off state gate-to-emitter voltages. In one arrangement, if the power devices within an active power semiconductor group 70 are in the on state, they can remain latched in the on state until a received current pulse from its respective secondary transformer controls them to switch to an off state, or vice versa.

[0046] Components within the electrical system 2 may be hardened to electromagnetic interference (EMI) to be more robust against the presence of electromagnetic waves in the air. Such EMI hardened components may prevent detected signals from propagating to the connected circuitry on the drive circuit 6.

Claims

1. A drive circuit, for driving a plurality of power semiconductor devices, comprising: a control module; a current pulse module connected to the control module and outputting current pulses; a plurality of pulse receiver modules; a first transformer unit having at least one primary transformer, the first transformer unit comprising a primary winding connected to the current pulse module, and a secondary winding; and a second transformer unit having a plurality of secondary transformers, each secondary transformer comprising a primary winding connected to the secondary winding of the first transformer unit, and a secondary winding connected to a respective one of the plurality of pulse receiver modules, in order to provide reflected current pulses to the respective one of the plurality of pulse receiver modules; wherein the first and second transformer units reduce parasitic coupling between the control module and the pulse receiver modules and minimize common mode currents flowing through the control module.

2. A drive circuit according to claim 1, wherein the first transformer unit comprises precisely one primary transformer comprising a primary winding and a secondary winding, wherein the primary winding of the first transformer unit is defined by the primary winding of the primary transformer and the secondary winding of the first transformer unit is defined by the secondary winding of the primary transformer.

3. A drive circuit according to claim 1, wherein the first transformer unit comprises a plurality of primary transformers, each primary transformer comprising a primary winding and a secondary winding, wherein the primary winding of the first transformer unit is defined by the primary winding of a first primary transformer and the secondary winding of the first transformer unit is defined by the secondary winding of a second primary transformer.

4. A drive circuit according to claim 3, wherein the secondary winding of the first primary transformer is connected to the primary winding of the second primary transformer or to the primary winding of a third primary transformer.

5. A drive circuit according to any preceding claim, further comprising a voltage loop connected to the primary winding or the secondary winding of the first transformer unit and connectable to a voltage reference node of an electrical system.

6. A drive circuit according to claim 3, further comprising a first voltage loop connected to the primary winding or the secondary winding of the first primary transformer and connectable to a first voltage reference node of an electrical system, and a second voltage loop connected to the primary winding or the secondary winding of the second primary transformer and connectable to a second voltage reference node of the electrical system.

7. A drive circuit according to claim 6, wherein the first voltage reference node and the second voltage reference node are the same.

8. A drive circuit according to any preceding claim, wherein the at least one primary transformer of the first transformer unit and/or the plurality of secondary transformers of the second transformer unit are implemented using toroids.

9. A drive circuit according to any preceding claim, wherein the current pulse amplifier module outputs current pulses based on one or more logic signals output by the control module.

10. A drive circuit according to any preceding claim, wherein the secondary windings of the second transformer unit are connected together in series.

11. An electrical system comprising: a drive circuit according to any preceding claim; and a plurality of active power semiconductor groups connected in series, each active power semiconductor group comprising one or more power devices and connected to a respective one of the plurality of pulse receiver modules; wherein each pulse receiver module commands the one or more power devices of the respective one of the plurality of active power semiconductor groups to turn on or off based on current pulses received from the respective secondary winding, and latches the current pulses.

12. An electrical system according to claim 11, wherein the drive circuit further comprises a voltage loop connected between the primary winding or the secondary winding of the first transformer unit and a voltage reference node of the electrical system.

13. An electrical system according to claim 12, wherein the voltage reference node is a midpoint of multiple series voltage references.

14. An electrical system according to claim 11, wherein the drive circuit further comprises a voltage loop connected between the primary winding or secondary winding of the first transformer unit and a node between two of the active power semiconductor groups.

15. An electrical system according to claim 11, wherein the first transformer unit comprises a plurality of primary transformers, each primary transformer comprising a primary winding and a secondary winding, and the drive circuit further comprises a first voltage loop connected between the primary winding or the secondary winding of a first primary transformer and a first node between a first two of the active power semiconductor groups, and a second voltage loop connected between the primary winding or the secondary winding of a second primary transformer and the first node or a second node between a second two of the active power semiconductor groups.

16. An electrical system according to claim 11, wherein the drive circuit further comprises a voltage loop connected between the primary winding or secondary winding of the first transformer unit and one of the active power semiconductor groups.

17. An electrical system according to claim 11, wherein the first transformer unit comprises a plurality of primary transformers, each primary transformer comprising a primary winding and a secondary winding, and the drive circuit further comprises a first voltage loop connected between the primary winding or the secondary winding of a first primary transformer and a first active power semiconductor group, and a second voltage loop connected between the primary winding or the secondary winding of a second primary transformer and the first active power semiconductor group or a second active power semiconductor group.

18. An electrical system according to claim 11, further comprising a DC link with one or more capacitors, and wherein the drive circuit further comprises a voltage loop cormected between the primary winding or the secondary winding of the first transformer unit and a midpoint of the DC link or another voltage node with respect to the one or more capacitors.

19. An electrical system according to claim 11, further comprising a DC link with one or more capacitors, wherein the first transformer unit comprises a plurality of primary transformers, each primary transformer comprising a primary winding and a secondary winding, and wherein the drive circuit further comprises a first voltage loop connected between the primary winding or the secondary winding of a first primary transformer and a midpoint of the DC link, and a second voltage loop connected between the primary winding or the secondary winding of a second primary transformer and the midpoint of the DC link or another voltage node with respect to the one or more capacitors.

20. An electrical system according to claim 11, further comprising a DC link with one or more capacitors, wherein the first transformer unit comprises a plurality of primary transformers, each primary transformer comprising a primary winding and a secondary winding, and wherein the drive circuit further comprises a first voltage loop connected between the primary winding or the secondary winding of a first primary transformer and a midpoint of the DC link or another voltage node with respect to the one or more capacitors, and a second voltage loop connected between the primary winding and the secondary winding of a second primary transformer and a node between two of the active power semiconductor groups.

21. An electrical system according to claim 11, further comprising a DC link with one or more capacitors, wherein the first transformer unit comprises a plurality of primary transformers, each primary transformer comprising a primary winding and a secondary winding, and wherein the drive circuit further comprises a first voltage loop connected between the primary winding or the secondary winding of a first primary transformer and a midpoint of the DC link or another voltage node with respect to the one or more capacitors, and a second voltage loop connected between the primary winding and the secondary winding of a second primary transformer and an active power semiconductor group.

22. A method, for driving an electrical system, comprising: outputting current pulses from a current pulse module controlled by a control module; receiving current pulses at a primary winding of a first transformer unit; communicating the current pulses to a secondary winding of the first transformer unit; receiving the current pulses at a plurality of primary windings of a second transformer unit; and communicating the current pulses to a plurality of secondary windings of the second transformer unit, each of the plurality of secondary windings of the second transformer unit being associated with a respective one of the plurality of primary windings of the second transformer unit and connected to a respective pulse receiver module; wherein the first and second transformer units reduce parasitic coupling between the control module and the pulse receiver modules and minimize common mode currents flowing through the control module.

23. A method according to claim 22, wherein the current pulses are based on one or more logic signals output by the control module.

24. A drive circuit substantially as herein described and with reference to the drawings.