Multiphase converter and method for phase load balancing - Patents.com

Abstract

A multi-phase converter (10) for phase load balancing includes a converter circuit (1) having three phase contacts (11) and performs closed-loop control of assigned input phase currents at each of the three phase contacts (11) to predetermined input phase current setpoints I1, I2, I3, where the input phase current setpoints I1, I2, I3 are determined as vector variables having current magnitudes I1, I2, I3, and phase shifts φ1, φ2, φ3, respectively, as follows: The magnitudes of the input phase current setting values ​​I1, I2, and I3 are equal to or less than the assigned maximum current magnitudes I1d, I2d, and I3d (hereinafter also referred to as current upper limit values), The power flowing into the converter circuit (1) is maximized at the phase contact (11), Furthermore, optionally, certain constraints on the phase shift of the input phase currents are satisfied.

Description

Detailed Description

[0001] The present invention relates to the field of electronic power converters. The present invention relates to a multiphase converter for balancing phase loads and to a method for balancing phase loads according to the preambles of the respective independent patent claims.

[0002] On-board charging devices for electric vehicles (called on-board chargers or OBCs) can be connected to a three-phase power supply if a corresponding power source is present. Ideally, the power requirements of each power supply phase are balanced, i.e., all phase currents supplied to the charging device are equal. For example, an 11 kW charging device for an electric vehicle connected to a power supply with a rated voltage of 3 x 230 V will draw 16 A per phase, which is sufficient for a full overnight charge.

[0003] However, the load capacity of one or more phases may be limited under certain circumstances due to other high loads, such as a hot water boiler or air conditioning equipment. For example, if the maximum current per phase is 20 A and a hot water boiler draws 10 A from one phase at night, the charging device must reduce the power on that phase to 10 A or less. This can be achieved by a three-phase charging system consisting of three single-phase charging devices, each connected as a load between a phase and the neutral conductor. Here, each of the three single-phase charging devices can implement a power factor correction (PFC) circuit to comply with regulations regarding harmonic limits on the respective phase current. Therefore, this three-phase charging system includes three PFCs, each connected between the phase and the neutral conductor.

[0004] WO 2018 / 176184 describes a voltage sampling circuit in a three-phase PCF power supply.

[0005] U.S. Patent No. 8,788,106 describes distributing power to multiple devices for deicing aircraft wings according to the power requirements of each device. These devices are resistive heating elements in a three-phase electrical system. The constraint on the operation of these devices is to maintain the neutral current below an upper limit.

[0006] EP 3 435 533 A1 describes a three-phase electrical system with individual AC-DC phase modules in a star connection on the AC side. A method for closed-loop control of the voltage at the star point is disclosed. A similar method is also described in AU 2015203405 A1. German Patent Application No. 102019105661 teaches balancing the asymmetric load of a multi-phase system with multiple consumers by first redistributing the consumers to the phases. Any remaining asymmetry is compensated for by active rectifiers supplying further consumers. The aim is to achieve a symmetric three-phase current system in the supply phases.

[0007] The object of the present invention is to provide a multiphase converter for phase load balancing of the type mentioned in the introduction, and a method for phase load balancing, which requires less circuit engineering effort on the power components compared to existing solutions.

[0008] This object is achieved by a multiphase converter for phase load balancing and a method for phase load balancing having the features of the respective independent patent claims.

[0009] A multi-phase converter is used for phase load balancing, comprising a converter circuit and a controller, the converter circuit having three or more phase contacts and configured to supply power to consumers, the controller configured to control the converter circuit to thereby perform closed-loop control of assigned input phase currents at each of the three phase contacts to predetermined input phase current setpoints I1, I2, I3.

[0010] Here, the controller is configured to determine input phase current setpoints I1, I2, I3 during operation of the converter circuit as vector variables having current magnitudes I1, I2, I3 and phase shifts φ1, φ2, φ3, respectively, as follows: The magnitudes of the input phase current setting values ​​I1, I2, and I3 are equal to or less than the assigned maximum current magnitudes I1d, I2d, and I3d (hereinafter also referred to as current upper limit values), The power flowing into the converter circuit at the phase contacts is maximized, Furthermore, optionally, certain constraints on the phase shift of the input phase currents are satisfied.

[0011] In this document, the converter circuit is described as having three phase contacts by way of example, however, it can also be realized with more than three phase contacts, in particular with six phase contacts.

[0012] The consumers may be supplied with power via the lower and upper contacts. The supply of power to the consumers may be achieved by a converter circuit configured to selectively direct current from each of the three phase contacts to the lower or upper contact. In particular, the converter circuit is configured to connect each of the three phase contacts to the lower or upper contact of one consumer.

[0013] The fact that the controller is configured to determine the input phase current setpoints as vector variables, each having a current magnitude and a phase shift, means that the input currents are sinusoidal, creating a three-phase system or a system with more than three phases.

[0014] This multiphase converter allows the input currents to be shaped to form a balanced system with three or more phases, without the need for a neutral conductor for balancing current. However, in particular, there is no actual star point in the converter circuit, so known approaches to controlling the converter circuit cannot be applied.

[0015] The cost and size of an EV charging system can be reduced by applying a three-phase charging system that does not require a neutral connection. As an example, a three-phase converter can be used as a PFC, and in the manner described herein, the converter can be controlled to create an asymmetric load that compensates for a given existing load on the power source, for example.

[0016] Due to the absence of a neutral conductor, the possibility of asymmetric phase loads is greatly reduced in three-phase PFC. Within this limited range, the described three-phase converter can obtain a desired power from the three-phase source while respecting the individual upper limits of all three phase currents. This may be the maximum available power. If this is not the case, one degree of freedom remains to obtain the desired power while balancing the loads on each phase as much as possible. These upper limits may be due to loading on each phase by other consumers.

[0017] A half-bridge branch may be provided for each input contact to selectively connect one of the input contacts to the lower or upper contact of the consumer. For this purpose, the half-bridge branch may include a lower switch and a lower flyback diode connected between the center tap of the half-bridge branch and the lower contact, and an upper switch and an upper flyback diode connected between the center tap of the half-bridge branch and the upper contact. The center tap may be connected to the corresponding input contact via a smoothing inductor.

[0018] Thus, in an embodiment, three or more phase contacts form primary contacts for feeding a multi-phase converter, said multi-phase converter not comprising a primary contact for a neutral conductor.

[0019] In an embodiment, the controller is configured in the verification step to determine whether the magnitudes of the input phase current set values ​​I1, I2, I3 are achievable as being equal to the assigned current upper limits I1d, I2d, I3d, respectively, and, if not achievable, to reduce the magnitude of the current corresponding to the largest of the current upper limits.

[0020] In a three-phase system, if the magnitude of the largest maximum current in terms of magnitude (current limit) is I3d, the verification step and possibly the adaptation performed is: I1=I1d and I2=I2d, and

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[0021] In an embodiment, the controller is configured to determine the current magnitudes of the input phase current setpoints I1, I2, I3 based on the magnitudes of the virtual delta currents J1, J2, J3, where the following formula applies:

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[0022] The maximum possible power due to limited phase currents is uniquely defined as the solution to this system of equations. Three input phase current setpoints I1, I2, and I3 are specified, and the magnitudes of the virtual delta currents J1, J2, and J3 are determined. In particular, the solution assumes that the phase shift of the current relative to the voltage is in the range of +30° to -30°, and the maximum current magnitude is I3=min{I3d;√(I1 2 +I1·I2+I2 2 )} It is unambiguous insofar as it is limited in accordance with

[0023] If the required power is lower than the maximum possible power, the operating point that results in the smallest power ripple can be selected.

[0024] Thus, in an embodiment, the multi-phase converter is configured to close-loop control the converter circuit for maximum power draw at the phase contacts using equal current magnitude constraints for the input phase current setpoints.

[0025] In an embodiment, the controller is configured to store or receive load limit information for at least one of the phase contacts and reduce the current upper limit of that phase contact according to the load limit information.

[0026] Further preferred embodiments are derived from the dependent patent claims, wherein features from the method claims may, where context permits, be combined with the device claims and vice versa. [Brief explanation of the drawings]

[0027] The subject matter of the invention will be explained in more detail below by means of preferred embodiments illustrated in the accompanying drawings, each of which is shown diagrammatically. [Figure 1] FIG. 1 is a diagram showing a charging device including a three-phase converter without a neutral point. [Figure 2] FIG. 2 shows a three-phase converter with assigned controllers. [Figure 3] FIG. 3 is a diagram showing voltages and currents at the phase contacts of a three-phase converter. [Figure 4] FIG. 4 shows a three-phase power supply with a given load between one phase and the star point. [Figure 5] FIG. 5 shows the currents in this power supply when the three-phase converter is optimized for maximum power intake. [Figure 6] FIG. 6 shows a three-phase power supply with a given load between one phase and the star point. [Figure 7] FIG. 7 shows the currents in this power supply when the three-phase converter is optimized for balanced supply currents. DETAILED DESCRIPTION OF THE INVENTION

[0028] Essentially, identical or similarly functioning parts are provided with the same reference numerals in the figures.

[0029] FIG. 1 shows a charging device including a three-phase converter (hereinafter also referred to as converter circuit 1) without a neutral point. Converter circuit 1 has an input side or power supply side with three phase contacts 11. Each of the phase contacts 11 is connected, typically via a choke, to a center tap of an assigned bridge branch 12. Each bridge branch 12 selectively connects the current of the respective phase contact to a lower contact 31 or an upper contact 32 of converter circuit 1. These contacts are connected by an intermediate circuit capacitance 33 and feed a DC-DC converter 4, which in turn feeds a battery 5. The internal structure of converter circuit 1 and DC-DC converter 4 is not critical for realization. Converter circuit 1 only needs to be able to set the currents through the phase contacts 11. In particular, a controller can be used to set the sinusoidal curves of each current, each with a configurable amplitude and phase shift.

[0030] 2 shows a converter circuit with an assigned controller 2. It comprises a gate signal generator 23, which generates: As control input signals, the amplitude and phase shift of the input phase currents I1, I2, I3 are received as set values; receive as measurements the measured phase currents I1a, I2a, I3a and phase voltages V1, V2, V3; A gate signal 24 is output to the converter circuit 1 as a command signal.

[0031] The set values ​​are determined by a pre-processing stage 21 which receives current upper limit values ​​I1d, I2d, I3d from a current maximum value acquisition unit 20. Input phase current set values ​​I1, I2, I3 are determined from these current upper limit values ​​in the pre-processing stage 21. From these, set values ​​for the phase shifts φ1, φ2, φ3 are determined in a phase shift evaluation unit 22.

[0032] The current upper limits I1d, I2d, I3d may be specified by the power grid from which the power is supplied and transmitted to the multi-phase converter 10. A power grid equipped with means for detecting consumption values, switching or controlling consumers, and transmitting data on the status of the power sources is known as a smart grid. Such a smart grid may thereby transmit the maximum obtainable power or the maximum allowed current per phase to the multi-phase converter 10.

[0033] At least one load (hereafter referred to as an external load), which may be static or may be switched on and off or dynamically change in a continuous manner, may be connected to one or more phases that also supply the multi-phase converter. The maximum current that the multi-phase converter can still draw is limited by this external load. For example, in the case of an 11 kW charging device, one of the phase currents may be limited to 10 A, while the others are not, i.e., the other phases may have a nominal phase current of 16 A. Information about the state of the external load may be incorporated by the smart grid into the current upper limits I1d, I2d, and I3d.

[0034] The pre-processing stage 21 verifies that: ·Are the upper current limits I1d, I2d, and I3d achievable? For example, the combination I3d=16A and I1d=I2d=6A cannot be realized. If not, what are the achievable current magnitudes I1, I2, I3 for the input phase current setpoints that result in the maximum charging power? In the example above, these are I3 = 10.4 A, I1 = I2 = 6 A, where: I3=min{I3d;√(I1 2 +I1·I2+I2 2 )} is.

[0035] The phase shift evaluation unit 22 determines the phase shifts φ1, φ2, and φ3 in the following manner, which is explained using FIG. 3. This represents the voltages and currents at the input terminals of the converter circuit 1. From the perspective of the phase contacts 11, the converter circuit 1 can be considered equivalent to a resistive delta circuit. This figure shows a phasor diagram combination of the voltages V1, V2, and V3 at the phase contacts 11 and the phase currents I1, I2, and I3 flowing into the phase contacts 11 (by convention, vector variables are printed in bold). Virtual delta currents with magnitudes J1, J2, and J3, each with a mutual phase shift of 120°, flow through the equivalent circuit. The delta currents are vectorially added to the incoming (phase) currents at the contacts of the equivalent circuit. Because there is no neutral conductor, the vector sum of the incoming currents must be zero. This condition and the vector sum lead to equations that determine the phase shifts φ1, φ2, and φ3 of the phase currents for given phase current magnitudes I1, I2, and I3. Applying the law of cosines, these equations become:

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[0036] These equations can generally all be solved by numerical approximations based on the magnitudes of the fictitious delta currents J1, J2, and J3. Analytical solutions are possible in the individual cases, for example, when two of the phase currents are equal. This is the case when an external load is connected to only one of the phases.

[0037] Using the magnitudes of the virtual delta currents J1, J2, and J3, and applying the cosine law to the virtual delta currents of FIG. 3, the phase shift of the input phase current setpoints is:

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[0038] The phase shift of the current relative to the voltage is in the range of +30° to -30°, and the maximum current magnitude is, for example, I3=min{I3d;√(I1 2 +I1·I2+I2 2 )} The solution is unique if it is assumed that the sigma is bounded according to

[0039] Mathematically equivalent methods may be performed that, in actual implementation, will yield the same results, for example, values ​​may be normalized to some current magnitude value when calculated.

[0040] If a particular operating condition is known in advance, the solution to the equation can be pre-calculated and stored in the controller, and retrieved when such an operating condition occurs. This may be the case, for example, when given an external load with only a limited number of load stages, such as a boiler that is turned on and off.

[0041] Therefore, starting from the specified current limits I1d, I2d, and I3d, and reducing the magnitude of the highest current, if necessary, so that each current complements the others and becomes zero, a physically feasible solution exists for the phase shift of the three currents. This results in the magnitudes of the input phase currents I1, I2, and I3. From this, the setpoints for the phase current phase shifts φ1, φ2, and φ3 are determined via the magnitude of the virtual delta current. These are used by the gate signal generator 23 for closed-loop control of the converter circuit 1. This results in maximum power capture by the converter circuit 1. The power capture can be calculated in a known manner as the sum of the powers flowing into the converter circuit 1 at each phase contact 11. This is the product of the voltage and current at each phase contact 11 multiplied by the cosine of the phase shift.

[0042] Figure 4 shows a three-phase power supply with a given load between one phase and the star point, and Figure 5 shows the current in this supply when the three-phase converter is controlled for maximum power draw. As an example, consider a 230V / 400V three-phase power supply. A uniform power load of 16A is achieved on each phase. The converter obtains a maximum possible power supply power of 9.5kW. However, due to an additional external load on the neutral conductor, one phase can only be loaded to a reduced extent.

[0043] As an alternative to maximum power draw, the phase currents can be selected to minimize ripple at the input of the converter circuit 1. For this purpose, the three input phase current setpoints I1, I2, I3 are set equal to each other and to the minimum of the three upper current limits I1d, I2d, I3d. The variation in power draw over the full wave ("power ripple") is thereby kept as small as possible.

[0044] Figure 6 shows the same three-phase power supply, and Figure 7 shows the current in this supply when the three-phase converter is controlled to balance power in the converter. Thus, uniform device loading of the converter is achieved. If all three phases have the same load at the device input, the highest possible power is 6.9 kW. In this case, all three phases draw current from the least loaded phase.

[0045] In embodiments, a compromise solution between maximum power draw and uniform device loading of the converter can be achieved. For example, if the required power is less than the maximum possible power, "best balancing" can be considered as the operating point that results in the smallest power ripple. One example is when the power is 6 kW, one phase current is limited to 10 A, and the other two are limited to 16 A. In that case, one phase can be loaded with 10 A and the other two with approximately 7.5 A, which creates power ripple. Alternatively, all three phases can be loaded with 8.7 A, which results in symmetrical loading and therefore ripple-free power.

[0046] Alternatively, closed loop control can be used to at least approximately uniformly load the source power supply (not shown), for which information about the load due to asymmetrical loading must exist.

Claims

1. A multi-phase converter (10) for phase load balancing comprising a converter circuit (1) and a controller (2), The converter circuit (1) has three or more phase contacts (11) and is configured to supply power to a consumer; a controller (2) configured to control the converter circuit (1) to thereby perform closed-loop control of assigned input phase currents in each of the three phase contacts (11) to predetermined input phase current setpoints I1, I2, I3; The controller (2) calculates the input phase current set values ​​I1, I2, I3 as vector variables each having a current magnitude I1, I2, I3 and a phase shift φ1, φ2, φ3 during operation of the converter circuit, The magnitudes of the currents of the input phase current setting values ​​I1, I2, and I3 are equal to or less than the assigned maximum current magnitudes I1d, I2d, and I3d (hereinafter also referred to as current upper limit values), respectively; - the power flowing into the converter circuit (1) at the phase contact (11) is maximized; and optionally, a predetermined constraint on the phase shift of the input phase currents is satisfied. A multi-phase converter (10) configured to determine:

2. 2. The multi-phase converter (10) of claim 1, wherein the three or more phase contacts (11) form primary contacts for supplying power to the multi-phase converter (10), and the multi-phase converter (10) does not include a primary contact for a neutral conductor.

3. The controller In a verification step, it is determined whether the magnitudes of the input phase current set values ​​I1, I2, and I3 can be realized as being equal to the assigned current upper limit values ​​I1d, I2d, and I3d, respectively; If not feasible, reduce the magnitude of the current corresponding to the largest current upper limit value among the current upper limits.

3. A multi-phase converter (10) according to claim 1 or 2, configured as follows:

4. The controller is configured to determine the current magnitudes of the input phase current setpoints I1, I2, I3 based on the magnitudes of virtual delta currents J1, J2, J3, and is configured to determine the current magnitudes of the input phase current setpoints I1, I2, I3 based on the magnitudes of virtual delta currents J1, J2, J3, using the following formula: I1 ２ =J1 ２ +J2 ２ +J1・J2、 I2 ２ =J2 ２ +J3 ２ +J2・J3、 I3 ２ =J3 ２ +J1 ２ +J3・J1 3. The multiphase converter (10) according to claim 1 or 2, wherein:

5. The controller adjusts the phase shift of the input phase current setpoint according to the following formula: φ1=30°-arccos{(I1 ２ +J1 ２ -J2 ２ ) / (2I1・J1)}、 φ2=30°-arccos{(I2 ２ +J2 ２ -J3 ２ ) / (2I2・J2)}、 φ3=30°-arccos{(I3 ２ +J3 ２ -J1 ２ ) / (2I3・J3)} The multi-phase converter (10) of claim 4, configured to determine:

6. 6. The multi-phase converter (10) according to claim 1, configured to perform closed-loop control of the converter circuit (1) for maximum power intake at the phase contacts (11) using a constraint that the magnitudes of the input phase current setpoints I1, I2, I3 are equal.

7. The multi-phase converter (10) according to any one of claims 1 to 6, wherein the controller (2) is configured to store or receive load limit information relating to at least one of the phase contacts (11) and reduce the current upper limit value of the phase contact (11) in accordance with the load limit information.

8. A method of operating a multi-phase converter (10) for phase load balancing, comprising a converter circuit (1) and a controller (2), comprising: The converter circuit (1) has three or more phase contacts (11) and is configured to supply power to a consumer; The method of operation, wherein the controller (2) controls the converter circuit (1) to close-loop control the assigned input phase currents at each of the three phase contacts (11) to predetermined input phase current setpoints I1, I2, I3, The controller (2) calculates the input phase current set values ​​I1, I2, I3 as vector variables each having a current magnitude I1, I2, I3 and a phase shift φ1, φ2, φ3, as follows: The magnitudes of the currents of the input phase current setting values ​​I1, I2, and I3 are equal to or less than the assigned maximum current magnitudes I1d, I2d, and I3d (hereinafter also referred to as current upper limit values), respectively; - the power flowing into the converter circuit (1) at the phase contact (11) is maximized; - further, optionally, predetermined constraints on the phase shifts of the input phase currents are satisfied; 10. A method of operating a multi-phase converter (10), comprising: determining:

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