Seven-switch indirect matrix converter with passive secondary circuit

Abstract

A direct current (DC) fast charger for charging batteries of electric vehicles (EVs), comprising a primary circuit with seven bidirectional switches, electrically connected to a primary wire of a transformer and configured to draw alternating current (AC) voltage; and a secondary circuit with a plurality of diodes arranged to rectify AC voltage to DC voltage, electrically connected to a secondary wire of the transformer, such that the DC fast charger unidirectionally converts alternating voltage drawn from the primary circuit into direct voltage output from the secondary circuit.

Description

GOVERNMENT INTEREST

[0001] This invention was made with government support under contract DE-EE0009869, awarded by the United States Department of Energy, Energy Efficiency & Renewable Energy EE-1 Office. The U.S. government retains certain rights in the invention. TECHNICAL FIELD

[0002] This application relates to electric vehicles (EVs) and, in particular, to chargers for charging EVs. BACKGROUND

[0003] Modern vehicles are increasingly powered at least partially or entirely by electric motors. These vehicles, often referred to as electric vehicles (EVs), include a vehicle battery and one or more electric motors that drive the vehicle's wheels. The vehicle batteries are periodically connected to a battery charger. As drivers purchase more and more EVs, they want to be able to charge the vehicle batteries relatively quickly. Therefore, faster and more efficient vehicle battery chargers are helpful. SUMMARY

[0004] In one implementation, a direct current (DC) fast charger for charging batteries of electric vehicles (EVs) includes a primary circuit having seven bidirectional switches electrically connected to a primary wire of a transformer and configured to source alternating current (AC) power; and a secondary circuit having a plurality of diodes arranged to rectify alternating current to direct current electrically connected to a secondary wire of the transformer, such that the DC fast charger unidirectionally converts alternating current sourced at the primary circuit to direct current output from the secondary circuit.

[0005] In another implementation, a DC fast charger for charging batteries of EVs includes a primary circuit having seven bidirectional switches electrically connected to a primary wire of a transformer and configured to source alternating current; a secondary circuit having a full-bridge rectifier comprising passive electrical components arranged to rectify alternating current to direct current, electrically connected to a secondary wire of the transformer, wherein the DC fast charger unidirectionally converts alternating current sourced at the primary circuit to direct current output from the secondary circuit.

[0006] In yet another implementation, a DC fast charger for charging batteries of EVs includes a primary circuit having seven bidirectional switches electrically connected to a primary wire of a transformer and configured to source alternating current; a shim inductor electrically connected to the primary circuit; a secondary circuit having a full-bridge rectifier comprising passive electrical components arranged to rectify alternating current to direct current and a capacitor electrically connected to a secondary wire of the transformer, wherein the DC fast charger unidirectionally converts alternating current sourced at the primary circuit to direct current output from the secondary circuit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram illustrating an implementation of an electric vehicle; Fig. 2 is a circuit diagram illustrating an implementation of a DC fast charger and control system; and The Fig. 3a-3f are circuit diagrams illustrating an implementation of a DC fast charger. DETAILED DESCRIPTION

[0007] A DC fast charger with a seven-switch indirect matrix converter for automotive applications is unidirectional, so it converts electrical power drawn from a grid and supplies the converted power to an electric vehicle (EV) for charging (G2V). The DC fast charger includes a primary circuit with a seven-switch topology with bidirectional switches. The secondary circuit of the DC fast charger can use a passive diode bridge instead of actively controlled switches, such as those with a gate that regulates conductivity, thereby reducing costs compared to other designs. The electrical power supplied to the DC fast charger is three-phase alternating current.

[0008] The seven-switch indirect matrix converter or DC fast charger can supply unidirectional electrical current from the three-phase mains at the primary circuit to the secondary circuit by controlling the modulation of a semi-square wave. In one implementation, the period of the three-phase AC mains, measured at 1 / 50–1 / 60 of a second (s), can be divided into several sectors, for example, six, each delimited by two consecutive inflection points of the AC zero-sequence voltage. In each sector, the phase with the highest absolute value can be designated as the conducting phase, and the other two phases can be used to apply a controlled voltage to the primary circuit. The electrical current applied to the primary circuit can then include three different duty cycles, each corresponding to a phase. x the duty cycle of the voltage V a -V bDy can be the duty cycle of the voltage V a -V c denote, and D0 can denote the duty cycle of a freewheeling phase when the seventh switch is active. The seventh switch can facilitate a 50% reduction in conduction loss during freewheeling periods under light electrical load. The electrical current applied to the primary circuit can be converted to direct current by the diode bridge of the secondary circuit. The secondary circuit can include an inductor and a capacitor to smooth the DC output from the secondary circuit.

[0009] In detail on Fig. 1, an implementation of an electrical system 10 is shown that includes an electrical grid 12 and an electric vehicle (EV) 14 that can either draw electrical power from or provide electrical power to the grid 12. The electrical grid 12 can include any of a number of electrical power generators and electrical delivery mechanisms. Electrical generators (not shown) generate alternating electrical power, which can then be transmitted a long distance from the electrical generator for residential or commercial use. The electrical generator can be coupled to the electrical grid 12, which transmits the alternating electrical power from the electrical generator to an end user, such as a residence or business. When the alternating electrical power is provided to the electrical grid 12, the electrical power can be at a relatively high voltage so that it can be transmitted over relatively long distances.Once the electrical power reaches a location where it will be used, electrical transformers (not shown) can be used to lower the voltage level before it is finally delivered to a home or business. In one implementation, the AC voltage level used is effectively 360-510 volts three-phase AC at 50-60 Hz. However, this voltage range can vary.

[0010] An EV charging station, referred to herein as a DC fast charger 16, may receive alternating electrical power from the grid 12, rectify the alternating electrical power to direct electrical power, and provide the direct electrical power to the EV 14. The DC fast charger 16 may be geographically fixed, such as a charging station located in a vehicle garage or vehicle parking lot. The DC fast charger 16 may include an input port that receives alternating electrical power from the grid 12 and transmits the alternating electrical power directly to the EV battery 22, bypassing an on-board vehicle battery charger 18 included in the EV 14. An electrical cable 20 may be removably connected to an electrical junction box on the EV 14 and electrically connect the DC fast charger 16 to the EV 14 such that direct electrical power may be transmitted between the DC fast charger 16 and the EV battery 22.The DC fast charger 16 can draw 480 VAC from the grid 12 and have a power rating of 60-360 kW, which is supplied to the EV 14. This type of DC fast charging can be referred to as Level 3 EV charging. However, the EV charging station can use different standards. The term "electric vehicle" or "EV" can refer to vehicles that are either fully or partially powered by electric motors. EV can refer to electric vehicles, plug-in electric vehicles, hybrid electric vehicles, and battery-powered vehicles. The EV battery 22 can provide direct electrical power, controlled by power electronics, to the electric motors that power the EV. The EV battery 22 or batteries are rechargeable and can include lead-acid, nickel-cadmium (NiCd), nickel-metal hydride, lithium-ion, and lithium-polymer batteries.A typical vehicle battery voltage range may be from 100 to 1000 VDC. A control system, implemented as computer-readable instructions executable by a microprocessor, may be stored in non-volatile memory and retrieved to control functionality of the DC fast charger 16. This is discussed in more detail below.

[0011] Fig. 2 illustrates an implementation of a DC fast charger 16 and a control system 24 used with the charger 16. The DC fast charger 16 is an indirect matrix converter including a primary circuit 26 and a secondary circuit 28 inductively coupled to each other via a transformer 30. The primary circuit 26 includes seven switches 32 electrically coupled to the grid 12 and a primary winding 34 of the transformer 30. The switches 32 may be implemented using bipolar transistors (BJTs) or field-effect transistors (FETs), such as insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), or gallium nitride transistors (GaN). The switches 32 may be bidirectional or reverse blocking, so that they are four-quadrant switches that can conduct positive or negative forward current and block positive or negative reverse voltage.Various circuit configurations can be used to implement such a switch, any of which could be implemented in the DC fast charger described here. In one implementation, each switch 32 includes an A-side MOSFET and a B-side MOSFET with gates that can be electrically connected to a microprocessor. Six switches 32a-f can be electrically coupled to three conductors of the electrical network PHA, PHB, PHC and nodes a, b, c of the primary circuit 26. Voltages of these three conductors can be represented as V. a , V b and V c A seventh switch 32g may be connected in parallel with switches 32e and 32f and with the primary winding 34 of transformer 32. Inductors 36 and a bulk capacitor 38 may be electrically connected to conductors PHA, PHB, PHC of network 12.

[0012] The secondary circuit 28 is electrically connected to a secondary winding 40 of the transformer 30. The circuit 28 includes a passive full-bridge rectifier, which may be implemented using four diodes D1-D4. The diodes in the secondary circuit 28 may be implemented using any of a variety of different types of diodes. The secondary circuit 28 may include an electrical filter with an inductor and a capacitor that smooths the output DC voltage. The EV battery 22 may be electrically connected to the diodes such that the secondary circuit 28 passively rectifies AC voltage induced by the secondary winding 40 to DC voltage, which is applied to the EV battery 22.

[0013] The control system 24 may be implemented using a microprocessor with outputs electrically connected to the gates 42 of the switches 32 in the DC fast charger 16. An implementation of the control system 24 is shown in Fig. 2. The control system 24 includes a phase-locked loop 44 that is electrically connected to the three conductors PHA, PHB, PHC of the network 12. The phase-locked loop 44 can be used to control the phase (θ Netz ) of the AC voltage drawn from the network 12. The phase can then be provided to a dq transformation block 46 to produce a signal in the rotating reference frame (d q ). A voltage regulator 48 can I q * using a target DC voltage level subtracted from a measured DC voltage level (V dc *-V dc ). I q * can be connected to a first current regulator 50 together with the q be provided to V q* to generate. I d * can be connected to a second current regulator 52 together with the q be provided to V d *. A dq-abc block 54 can receive Vq*, Vd* and the phase (θ Netz ) minus an angular offset to a voltage source inverter (VSI) space vector modulation (SVM) block 56. The VSI-SVM block 56 may provide an output to a current source inverter (CSI) SVM block 58, which may provide an output to a matrix SVM block 60. Gate signals may be generated at block 62 and electrically communicated to the gates of the switches 32 to control the conduction state.

[0014] The DC fast charger 16 can control the primary circuit 26 to induce the flow of alternating current in the transformer 30. The change in the conductivity of the switches 32 included in the primary circuit 26 is shown in the Fig. 3a-f. An initial switching state of the primary circuit 26 is shown in Fig. 3a, where the A- and B-MOSFETs of switches 32a and 32d are initially conductive to allow current to flow through conductors A and B. The current path and conductivity of the switch are shown with arrows and / or dashed lines. An initial switching step can render the A-side MOSFETs of switches 32a and 32d non-conductive, as shown in Fig. 3b. A second switching step can make the B-side MOSFET of the seventh switch 32g conductive, as shown in Fig. 3c. A third switching step is shown in Fig. 3d shows the B-side MOSFET of switch 32a rendered non-conductive, the B-side MOSFET of switch 32c rendered conductive, and the B-side MOSFET of switch 32d rendered non-conductive. The conduction state changes of switches 32a, 32c, and 32d can be considered soft switching events because they occur without the presence of electrical current. Fig. 3e represents a fourth switching state in which the B-side MOSFET of switch 32g is rendered non-conductive. A fifth switching state is shown in Fig. 3f, where the A-side MOSFET of switch 32c is made conductive and the A-side of switch 32b is made conductive. The control system 24 can then return the conduction state of the primary circuit 26 to the initial switching state and repeat the five switching states to change the frequency of the AC voltage drawn from the mains 12.

[0015] It is to be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but is defined solely by the following claims. Furthermore, statements contained in the foregoing description refer to particular embodiments and are not to be construed as limitations on the scope of the invention or the definition of terms used in the claims, unless a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will be apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to be within the scope of the appended claims.

[0016] As used in this specification and the claims, the terms "e.g.," "for example," "for instance," "such as," and "like," and the verbs "comprise," "have," "include," and their other verb forms, when used in connection with an enumeration of one or more components or other items, are each to be construed as open-ended, meaning that the enumeration is not to be considered as excluding other, additional components or items. Other terms are to be interpreted as broadly as possible unless used in a context that requires a different interpretation. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EE 0009869

[0001]

Claims

[1] Direct current (DC) fast charger for charging batteries of electric vehicles (EVs), comprising: a primary circuit having seven bidirectional switches electrically connected to a primary wire of a transformer and configured to receive alternating current (AC) voltage; and a secondary circuit having a plurality of diodes arranged to rectify AC voltage to DC voltage, which is electrically connected to a secondary wire of the transformer, wherein the DC fast charger unidirectionally converts AC voltage sourced at the primary circuit into DC voltage output from the secondary circuit. [2] The DC fast charger according to claim 1, wherein the primary circuit uses the primary wire of the transformer as a stray inductance. [3] A DC fast charger according to any one of the preceding claims, wherein the secondary circuit includes an inductor and a capacitor. [4] DC fast charger according to any one of the preceding claims, further comprising a control system, wherein the control system is electrically connected to the seven bidirectional switches, which changes the frequency of the alternating voltage drawn from the mains in five switching state changes, and / or the control system is designed to divide three-phase alternating voltage drawn from the primary circuit into a plurality of sectors, each defined by two consecutive inflection points at which alternating voltage is equal to zero. [5] A DC fast charger according to claim 4, wherein the control system determines a sector with the highest absolute voltage. [6] Direct current (DC) fast charger for charging batteries of electric vehicles (EVs), comprising: a primary circuit having seven bidirectional switches electrically connected to a primary wire of a transformer and configured to receive alternating current (AC) voltage; a secondary circuit having a full-bridge rectifier comprising passive electrical components arranged to rectify AC voltage to DC voltage, which is electrically connected to a secondary wire of the transformer, wherein the DC fast charger unidirectionally converts AC voltage sourced at the primary circuit into DC voltage output by the secondary circuit. [7] The DC fast charger of claim 6, wherein the primary circuit uses the primary wire of the transformer as a leakage inductance. [8] A DC fast charger according to any one of claims 6 or 7, wherein the secondary circuit includes an inductor and a capacitor. [9] DC fast charger according to any one of claims 6 to 8, further comprising a control system,a wherein the control system is electrically connected to the seven bidirectional switches, which changes the frequency of the alternating voltage drawn from the mains in five switching state changes, and / or the control system is designed to divide three-phase alternating voltage drawn from the primary circuit into a plurality of sectors, each defined by two consecutive inflection points at which alternating voltage is equal to zero. [10] A DC fast charger according to claim 9, wherein the control system determines a sector with the highest absolute voltage.

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