Active rectifier circuit

Abstract

In a Vienna type rectifier circuit, a phase leg bridge circuit uses a cascode arrangement with three series connected controllable semiconductor switches driven by a single gate driver unit.

Description

Technical Field

[0001] The present invention relates to an active rectifier circuit for converting between single-phase or multi-phase AC voltage and DC voltage. Background Art

[0002] Typical grid connected power electronic devices, such as battery chargers, motor drives or AC coupled switch mode power supplies (SMPS), use active or passive power factor correction units to meet different grid codes. Active power factor correction units or active front-end converters - often referred to as active rectifiers - use controllable semiconductor switches to achieve their functions.

[0003] A well-known three-phase power factor correction topology is a unidirectional three-level rectifier known as the Vienna rectifier, which has advantages over the traditional six-switch bridge topology. The Vienna rectifier topology uses a switch arrangement to provide a controllable boost connection. This controllable connection must be able to block voltages of both polarities. In the basic Vienna rectifier setup, this is achieved by arranging a single controllable semiconductor switch in the rectifier diode bridge. Alternative Vienna-type topologies (NPFC, SPFC, ANPFC) use more than one power semiconductor and accompanying gate driver unit. Summary of the invention

[0004] It is an object of the present invention to provide an active rectifier circuit having reduced complexity and a reduced number of components.

[0005] The rectifier circuit according to the present invention comprises one or more bridge circuits. Each bridge circuit comprises, in sequence: a first series connection, comprising a first diode and a second diode; a first midpoint between the first diode and the second diode, forming an AC terminal of the rectifier circuit; and a second series connection, comprising a first semiconductor switch arrangement and a second semiconductor switch arrangement. The first series connection and the second series connection are arranged in parallel by being connected at an upper node and a lower node. A third diode is connected to the upper node and a fourth diode is connected to the lower node.

[0006] The first semiconductor switch arrangement comprises a series connection of a first controllable semiconductor switch and a second controllable semiconductor switch, wherein a gate node of the second controllable semiconductor switch is connected to a first load terminal of the first controllable semiconductor switch, and the first load terminal is connected to a lower node. The second semiconductor switch arrangement comprises a third controllable semiconductor switch, wherein a gate node of the third controllable semiconductor switch is connected to the lower node.

[0007] The rectifier circuit further comprises a capacitor series comprising two capacitors connected between the third diode and the fourth diode, a second midpoint between the capacitors being connected to a third midpoint between the semiconductor switch arrangements.

[0008] Advantageously, the rectifier circuit of the present invention uses a cascode structure for the first, second and third controllable semiconductor switches. In this way, the conventional arrangement of two controllable semiconductor switches as used in a symmetrical boost PFC, both of which require their own gate driver unit, is replaced by an arrangement of three series-connected controllable semiconductor switches, only one of which requires a gate driver unit. In this way, the complexity and cost associated with providing a gate driver unit for the rectifier circuit is reduced. The advantages of the three-level topology over the conventional 6-switch bridge and the advantages of the symmetrical boost PFC are retained.

[0009] The term "controllable semiconductor switch" is used to denote a power semiconductor element, such as a JFET, MOSFET or IGBT, which comprises two load terminals and a control (gate) terminal allowing control of the conduction state across the load terminals.

[0010] Other features that may be added alone or together in exemplary embodiments of the present invention include:

[0011] By having a single bridge circuit, the rectifier can be adapted to operate with a single-phase AC voltage. It can alternatively also be adapted to operate with a multi-phase AC voltage by providing more than one bridge circuit. In this case, the bridge circuits are connected in parallel, each bridge circuit being connected to a respective AC voltage phase, and the third midpoints of each bridge circuit being interconnected.

[0012] The AC terminals may be connected to an AC voltage across the inductive element to provide a voltage boost function.

[0013] The rectifier circuit may include a voltage controlled diode in the form of an avalanche diode or a Zener diode, or a series connection of those voltage controlled diodes between the gate node and the lower node of the third controllable semiconductor switch, which serves to protect the gate node of the third controllable semiconductor switch from excessive voltage differences to its (source) load node.

[0014] The first controllable semiconductor switch may be an enhancement mode semiconductor switch.This advantageously provides a normally-off functionality for the arrangement of the first and second switch arrangements, since the gate connections of the second and third controllable semiconductor switches ensure that these devices are turned off when the first controllable semiconductor switch is turned off.

[0015] The second and third controllable semiconductor switches may be depletion mode semiconductor switches.Some technically most advanced switches are currently only available as normally-on devices or have normally-on devices as their most advantageous form.

[0016] The second and third controllable semiconductor switches may be gallium nitride (GaN) HEMT or silicon carbide (SiC) JFET type switches. In addition, the second and third controllable semiconductor switches may have the same type and voltage rating. The first controllable semiconductor switch may be a silicon-MOSFET device. The first controllable semiconductor switch may have a lower voltage rating than the second and third controllable semiconductor switches. For example, the first controllable semiconductor switch may have a voltage rating of only 30V, while the second and third controllable semiconductor switches may have a voltage rating of 650V. In this way, the rectifier can be constructed to operate at a DC link voltage of, for example, 800 volts, while still using only a single gate driver unit driving the low voltage switch.

[0017] The rectifier circuit may include a gate driver unit connected to the gate node of the first controllable semiconductor switch. In this way, a cascode-like structure is used as the first switch arrangement. The first and second switch arrangements also serve as extended cascode structures. Turning off the first controllable semiconductor switch by the gate driver unit will cause the second and third controllable semiconductor switches to also be turned off. Turning on the first controllable semiconductor switch will cause the second and third controllable semiconductor switches to be turned on. A single gate driver unit can advantageously be the only gate driver unit for one bridge circuit.

[0018] The gate driver unit is connected to a control device which controls the operation of the gate driver unit or (in the case of a plurality) a plurality of gate driver units, thereby controlling the operation of the rectifier circuit. The control device is arranged to control the gate driver unit to perform a pulse width modulated switching scheme which operates in both half waves of the connected AC voltage and performs a voltage boost across the capacitor to a predefined DC voltage, thereby resulting in a predefined DC output voltage.

[0019] In an alternative arrangement, the rectifier circuit may include a gate driver unit connected to the gate node of the second controllable semiconductor switch and a separation diode connected between the gate node and the lower node of the second controllable semiconductor switch. In this arrangement, the second controllable semiconductor switch is directly controlled, rather than indirectly controlled via the first controllable semiconductor switch, which results in a reduction in switching times. The third controllable semiconductor switch is again indirectly controlled, such as in a cascode configuration.

[0020] In this arrangement, if the first controllable semiconductor switch is an enhancement mode device, the gate node of the first controllable semiconductor switch can be connected to a fixed supply voltage. In this way, the first controllable semiconductor switch remains in a conductive state throughout operation. If the supply voltage is removed from operation, such as in a fault condition, the first controllable semiconductor switch will automatically turn off, which will automatically cause the second and third controllable semiconductor switches to also turn off.

[0021] Furthermore, the connection between the gate node of the first controllable semiconductor switch and the supply voltage may include a switching component to cut off the connection in certain operating situations. The switching component may be a low speed switching component which is not a gate driver unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments of the present invention will now be described with reference to the accompanying drawings, but the present invention is not limited to the accompanying drawings. The description of the accompanying drawings is schematic. Note that in different drawings, similar or identical elements are marked with the same reference numerals.

[0023] Figure 1 A Vienna rectifier circuit known in the prior art is shown;

[0024] Figure 2 A bridge circuit of a Vienna-type rectifier known in the prior art is shown;

[0025] Figures 3 to 5 A rectifier circuit according to an embodiment of the present invention is shown.

[0026] Reference numerals list

[0027] 10 Vienna Rectifier

[0028] 30, 50, 100 rectifier

[0029] 121…123, 32, 51 bridge circuit

[0030] 131…133 AC voltage phase

[0031] 14 DC Link

[0032] 151, 152 DC terminal

[0033] 16 DC link midpoint

[0034] 171…173 Diode bridge rectifier

[0035] 181…183, 241, 242 Controllable semiconductor switches

[0036] 221 Bridge Circuit

[0037] 222 Four-element-bridge rectifier

[0038] 231, 232, 331, 332, 381, 382 diodes

[0039] 239, 251, 252 Gate driver unit

[0040] 34 Inductor

[0041] 35, 36 Depletion Mode Switch

[0042] 37 Enhanced Switch

[0043] 52 Supply voltage terminal

[0044] 53 Decoupling diode

[0045] 102 Cascode Circuit

[0046] 103…106 Rectifier switch

[0047] 107, 108 controllable switch DETAILED DESCRIPTION

[0048] Figure 1 A Vienna rectifier 10 known from the prior art is shown in FIG. The rectifier 10 of this example is suitable for connection to a three-phase AC network. It comprises three parallel arms for the three phases 131 ... 133. The arms are connected to a DC link 14 having upper and lower DC terminals 151, 152. The DC link 14 comprises two capacitors arranged in series connection with a midpoint 16, wherein the midpoint 16 is also connected to the arms.

[0049] Each arm comprises a bridge circuit 121 ... 123 with a 4-diode-bridge rectifier 171 ... 173, one input terminal of which is connected to the corresponding AC voltage phase 131 ... 133 and the other input terminal is connected to the DC link midpoint 16. Controllable semiconductor switches 181 ... 183 are arranged between the output terminals of the 4-diode-bridge rectifiers 171 ... 173. The output terminals of the 4-diode-bridge rectifiers 171 ... 173 are connected to the upper and lower DC terminals 151, 152 across further diodes.

[0050] Figure 2 The prior art known for Figure 1 An alternative bridge circuit 221 for the rectifier shown in FIG. Figure 2The bridge circuit 221 can be used to replace the bridge circuits 121 ... 123. The bridge circuit 221 is constructed in a similar manner to the bridge circuits 121 ... 123. Instead of the 4-diode bridge rectifiers 171 ... 173, it has a 4-element bridge rectifier 222, which includes two diodes 231, 232 and two controllable semiconductor switches 241, 242. The bridge circuit 221 does not have controllable semiconductor switches 181 ... 183.

[0051] although Figure 2 The alternative bridge circuit 221 is generally used more Figure 1 . . 123 has fewer components, but for two controllable semiconductor switches 241 , 242 , it requires the use of two gate driver units 251 , 252 .

[0052] Figure 3 An embodiment of the broad concept of the present invention is shown. Figure 3 A single-phase rectifier circuit 100 is shown. The rectifier circuit 100 is based on the rectifier circuit 221, but uses a common source and common gate circuit 102 instead of Figure 1 and 2 The bridge circuit shown in .

[0053] The cascode circuit 102 includes a series connection of two controllable switches 107, 108, wherein the gate contact of the upper portion of the switch 107 is connected to the source terminal of the lower portion of the controllable switch 108 across the avalanche diode 40. The rectifier circuit 100 also includes rectifier switches 103 ... 106 arranged in a manner similar to the bridge circuit 221. More specific embodiments of this general concept are described in Figure 4 and Figure 5 Shown and explained in.

[0054] Figure 4 A single-phase rectifier circuit 30 according to an embodiment of the present invention is shown. The rectifier circuit 30 uses a corresponding bridge circuit 32 instead of Figure 1 and Figure 2 The bridge circuit shown in .

[0055] The bridge circuit 32 comprises a first series connection of two diodes 331, 332. A first midpoint between the diodes 331, 332 forms an AC input terminal which is connected across the inductive element 34 to the phase of the AC voltage.

[0056] The bridge circuit 32 also includes a second series connected in parallel with the first series. The second series includes first and second lower controllable semiconductor elements 36, 37 connected in series and an upper third controllable semiconductor element 35. A second midpoint between the upper and lower controllable semiconductor elements 35 ... 37 is connected to the midpoint 16 of the DC link 14.

[0057] The upper connection points of the first and second series are connected to the upper DC terminal 151 across a diode 381. The lower connection points of the first and second series are connected to the lower DC terminal 152 across a diode 382.

[0058] The second series-connected upper controllable semiconductor element 35 and the second lower controllable semiconductor element 36 are normally-on (depletion mode) semiconductors. An example of such a device is a normally-on gallium nitride high electron mobility transistor (gallium nitride high electron mobility transistor). The first lower controllable semiconductor element 37 in turn is a normally-off (enhancement mode) semiconductor, such as an enhancement mode silicon-MOSFET. In this embodiment, the second and third semiconductor elements 35, 36 each have a voltage rating of 650 volts, while the first semiconductor element 37 is a low voltage device having a voltage rating of only 30 volts.

[0059] The bridge circuit 32 comprises a single gate driver unit 39 which is connected to the gate contact of the first lower controllable semiconductor element 37 and allows full control of the operation of this semiconductor element 37 .

[0060] The gate contacts of both the upper controllable semiconductor element 35 and the second lower controllable semiconductor element 36 are connected to the source contact of the first lower controllable semiconductor element 37 and thus to the lower connection point of the first and second series. In the case of the upper controllable semiconductor element 35, the connection includes an avalanche diode 40, which is selected to offset most of the voltage maintained by the lower DC link capacitor during rectifier operation to protect the gate from overvoltage, leaving only 10-20V between the gate and source contacts of the second semiconductor element 36. For example, in a rectifier circuit where the DC link voltage across the two capacitors is 800 volts, the avalanche diode may be selected to offset 380 volts. The avalanche diode 40 may include a series connection of two or more diodes to obtain the required voltage.

[0061] During operation, all switches of the bridge formed by the first to third semiconductor elements 35 ... 37 are controlled in cascode operation by the gate driver unit 39 via the first semiconductor element 37. All three switches 35 ... 37 are thus switched on and off together.

[0062] Figure 5 An alternative arrangement according to another embodiment of the invention is shown. Figure 5A single-phase rectifier circuit 50 is shown which is largely similar to the single-phase rectifier circuit 30. In contrast to the single-phase rectifier circuit 30, a single gate driver unit 39 is connected to the gate node of the second semiconductor switch 36. Furthermore, a decoupling diode 53 is connected between the gate node of the second semiconductor switch 36 and the lower connection point of the first and second series connection.

[0063] In this embodiment, the gate driver unit 39 drives the second lower controllable semiconductor element 36 directly, rather than indirectly via the first semiconductor element 37. To make this possible, the gate node of the first lower controllable semiconductor element 37 is directly connected to the supply voltage terminal 52. Thus, the first lower controllable semiconductor element 37 is in a permanently on-state as long as the supply voltage is present.

[0064] When the supply voltage is not present, for example due to a fault in the rectifier circuit, the first lower controllable semiconductor element 37 will be turned off. Since the gate node of the second semiconductor element 36 is connected via the decoupling diode 53 and in the presence of the AC input voltage, this gate node will be at a lower voltage than the source node of the second semiconductor element 36, thereby turning off the second semiconductor element 36. The third semiconductor element 35 will also be turned off as shown in FIG. Figure 4 In this way, the Figure 4 The normally closed operation of the embodiment of FIG. 1 is achieved while using only a single gate driver unit 39 . In addition, the second semiconductor element 36 is directly controlled by the gate driver unit 39 .

[0065] Thus, both described embodiments of the invention make it possible to drive a series combination of two semiconductor switches 35, 36 in a Vienna type rectifier circuit with a single gate driver unit 39. This results in a highly efficient circuit, allowing higher voltage capabilities compared to a single switch Vienna rectifier topology, while keeping the circuit complexity low.

Claims

1. A rectifier circuit (30, 50), comprising one or more bridge circuits (32, 51), each bridge circuit (32, 51) comprising: a first series connection comprising a first diode and a second diode (231, 331, 232, 332), a first midpoint between the first diode and the second diode (231, 331, 232, 332) forming an AC terminal of the rectifier circuit (30, 50), a second series comprising a first semiconductor switch arrangement and a second semiconductor switch arrangement, said first series and said second series being arranged in parallel, - a third diode (381) connected to the upper node of the first series connection and the second series connection, - a fourth diode (382) connected to the lower node of the first series connection and the second series connection, wherein - the first semiconductor switch arrangement comprises a series connection of a first controllable semiconductor switch and a second controllable semiconductor switch (36, 37), wherein a gate node of the second controllable semiconductor switch (36) is connected to a first load terminal of the first controllable semiconductor switch (37) and the first load terminal is connected to the lower node, and - the second semiconductor switch arrangement comprises a third controllable semiconductor switch (35), wherein a gate node of the third controllable semiconductor switch (35) is connected to the lower node across an avalanche diode (40) or a Zener diode, And wherein the rectifier circuit (30, 50) further comprises a capacitor series, the capacitor series comprising two capacitors connected between the third diode and the fourth diode (381, 382), a second midpoint (16) between the capacitors being connected to a third midpoint between the semiconductor switch arrangements.

2. The rectifier circuit (30, 50) according to claim 1, wherein the first controllable semiconductor switch (37) is an enhancement mode semiconductor switch.

3. The rectifier circuit (30, 50) according to claim 1, wherein the second controllable semiconductor switch and the third controllable semiconductor switch (35, 36) are depletion-mode semiconductor switches.

4. The rectifier circuit (30, 50) of claim 3, wherein the second controllable semiconductor switch and the third controllable semiconductor switch (35, 36) are gallium nitride HEMT or silicon carbide JFET switches.

5. The rectifier circuit (30, 50) according to any one of claims 1 to 4, comprising a gate driver unit (39) connected to a gate node of the first controllable semiconductor switch (37).

6. The rectifier circuit (30, 50) according to any one of claims 1 to 4, comprising a gate driver unit (39) connected to the gate node of the second controllable semiconductor switch (36) and a decoupling diode (53) connected between the gate node of the second controllable semiconductor switch (36) and the lower node.

7. The rectifier circuit (30, 50) of claim 6, wherein a gate node of the first controllable semiconductor switch (37) is connected to a supply voltage terminal (52).

Images