Multi-phase converter and method for phase load balancing

Abstract

A multiphase converter (10) for phase load balancing comprises a converter circuit (1) having phase contacts (11) and closed-loop control of an input phase current specified in each of the three phase contacts (11) to achieve a predetermined input phase current setpoint I1, I2, I3. Here, the input phase current setpoints I1, I2, I3 are determined as vector variables, each having a current amplitude I1, I2, I3 and a phase shift [phi] 1, [phi] 2, [phi] 3, such that the current amplitudes of the input phase current setpoints I1, I2, I3 are respectively less than or equal to specified maximum current limits I1d, I2d, I3d, below which are also referred to as current limits; the power flowing into the converter circuit (1) at the phase contacts (11) is maximized; and, optionally, prescribed constraints on the phase shift of the input phase current are satisfied.

Description

Technical Field

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

[0002] Onboard charging units for electric vehicles (referred to as onboard chargers, or OBCs) can be connected to a three-phase power supply, provided a suitable power source is available. Ideally, the power demand on each phase is balanced, meaning that equal current is supplied to the charging unit across all phases. For example, an 11 kW charging unit for an electric vehicle on a nominal voltage of 3 × 230 V draws 16 A per phase, which is sufficient for a full charge overnight.

[0003] However, in certain situations, the load capacity of one or more phases may be limited, for example due to other high loads (such as hot water boilers, air conditioning equipment, etc.). For example, if the maximum current per phase is 20 A, and the hot water boiler draws 10 A from a phase at night, the charger must reduce the power of that phase to 10 A or less. This can be achieved with a three-phase charger consisting of three single-phase chargers, each connected as a load between the phase and neutral conductors. Here, each of the three single-phase chargers can implement a power factor correction circuit (PFC) to comply with regulations regarding limiting the harmonics of the corresponding phase current. Therefore, the three-phase charger contains three PFCs, one between the phase and neutral conductors.

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

[0005] US 8'788'106 B2 describes a method for de-icing aircraft wings by distributing electrical power to multiple devices based on the power requirements of each device. The devices are resistive heating elements in a three-phase electrical system. The devices operate under the constraint that the neutral conductor current be kept below a limit.

[0006] EP 3 435 533 A1 describes a three-phase electrical system with independent AC-DC phase modules in a star configuration 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. Summary of the Invention

[0007] The object of the present invention is to provide a multiphase converter for phase load balancing and a method for phase load balancing of the type mentioned above, which require less expenditure on circuit technology with respect to power components than 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] This multiphase converter is used for phase load balancing. It includes a converter circuit and a controller. The converter circuit includes three or more phase contacts and is designed to supply power to an electrical device. The controller is designed to control the converter circuit and thereby perform closed-loop control of a specified input phase current in each of the three phase contacts to achieve predetermined input phase current set values ​​I1, I2, and I3.

[0010] Here, the controller is designed to determine the input phase current set values ​​I1, I2, I3 as vector variables when the converter circuit is operating, each vector variable having a current amplitude I1, I2, I3 and a phase shift φ1, φ2, φ3 such that

[0011] • The current amplitudes of the input phase current settings I1, I2, and I3 are respectively less than or equal to the specified current limits I1d, I2d, and I3d (hereinafter also referred to as current limits);

[0012] • The power flowing into the converter circuit at the phase contacts is maximized;

[0013] • and, optionally, satisfying specified constraints on the phase shift of the input phase currents.

[0014] Here and hereinafter, the converter circuit is described by way of example as comprising three phase contacts. However, it can also be realized with more than three phase contacts, in particular with six phase contacts.

[0015] Power can be supplied to the power consumer via the lower and upper contacts. Powering the power consumer can be achieved via a converter circuit designed to selectively direct current from each of the three phase contacts to either the lower or upper contact. Specifically, the converter circuit is configured to connect each of the three phase contacts to either the lower or upper contact of a power consumer.

[0016] The controller is designed to determine the input phase current setpoints as vector variables each having a current magnitude and a phase shift, which means that the input current is a sine wave and forms a three-phase system or a system with more than three phases.

[0017] This multiphase converter can be used to shape the input currents to form a balanced system with three or more phases, without requiring current balancing via a neutral conductor. However, a true neutral point does not exist in the converter circuit. Therefore, known methods for controlling converter circuits cannot be applied.

[0018] By implementing a three-phase charging system that does not require a neutral contact, the cost and size of EV charging equipment can be reduced. For example, a three-phase converter can be used as a PFC and controlled as described herein to create, for example, an asymmetrical load to compensate for a given existing load on the power supply.

[0019] Because there's no neutral line, using three-phase PFC significantly reduces the potential for asymmetrical phase loading. Within these limits, the three-phase converter can be used to obtain a specified power from the three-phase supply, taking into account the individual limits of all three phase currents. This can be the maximum available power. If not, a degree of freedom remains to achieve the required power while balancing the loads on each phase as closely as possible. These limits may be due to the loads on each phase imposed by other consumers.

[0020] To selectively connect an input contact to the lower or upper contact of a consumer, a half-bridge branch can be assigned to the corresponding input contact. To this end, a half-bridge branch can 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 can be connected to the corresponding input contact via a smoothing inductor.

[0021] Thus, in an embodiment, three or more phase contacts form the primary side contacts for supplying power to the multiphase converter, and the multiphase converter does not comprise a primary side contact for the neutral line.

[0022] In an embodiment, the controller is designed to determine in a verification step whether current amplitudes of the input phase current set values ​​I1, I2, I3 can be achieved, wherein these current amplitudes are respectively equal to the specified current limits I1d, I2d, I3d, and otherwise, to reduce the current amplitude that is the largest of the current limits.

[0023] In a three-phase system, assuming that the magnitude of the maximum current amplitude is represented by I3d, the verification step and possible adjustments can be made by setting I1 = I1d, I2 = I2d, and Therefore, the verification step is equivalent to checking whether I3d is less than the square root term.

[0024] In an embodiment, the controller is designed to determine the current amplitudes of the input phase current setpoints I1, I2, I3 based on the virtual triangle current amplitudes J1, J2, J3, wherein the following formula applies:

[0025] ,

[0026] ,

[0027] .

[0028] The maximum possible power based on the limited phase currents is explicitly defined as the solution to this system of equations. The three input phase current setpoints I1, I2, I3 are specified, and the virtual triangle current amplitudes J1, J2, J3 are determined. Specifically, if it is assumed that the phase shift of the current relative to the voltage is in the range of +30° to -30°, and the maximum current amplitude is calculated according to If we restrict , the solution is clear.

[0029] If the required power is lower than the maximum possible power, the operating point can be chosen such that the power ripple is minimized.

[0030] To this end, in an embodiment, the multiphase converter is designed for closed-loop control of the converter circuit to achieve maximum power dissipation at the phase contacts, with the constraint that the current amplitudes of the input phase current setpoints are equal.

[0031] In an embodiment, the controller is configured to store or receive load limit information of at least one phase contact, and reduce the current limit value of the phase contact according to the load limit information.

[0032] Further advantageous embodiments can be derived from the dependent patent claims. In this context, features of method claims can be combined with device claims where appropriate, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The subject matter of the present invention will be explained in more detail below by the preferred embodiments shown in the accompanying drawings. Each embodiment is shown in schematic form:

[0034] Figure 1 A charging device with a three-phase converter without a neutral point is shown;

[0035] Figure 2 A three-phase converter with a specified controller is shown;

[0036] Figure 3 shows the voltage and current at the phase contacts of a three-phase converter;

[0037] Figure 4 A three-phase supply with specified loads between the phases and the star point is shown;

[0038] Figure 5 shows the current in the power supply when the three-phase converter is optimized for maximum power consumption;

[0039] Figure 6 shows a three-phase supply with specified loads between the phases and the star point; and

[0040] Figure 7The currents in the power supply are shown when the three-phase converter is optimized to achieve supply current balance.

[0041] Generally, functionally identical or equivalent components are provided with the same reference numerals in the figures. DETAILED DESCRIPTION

[0042] Figure 1 A charging device with a three-phase converter without a neutral point (hereinafter also referred to as converter circuit 1) is shown. Converter circuit 1 includes an input or power supply side with three phase contacts 11. Each phase contact 11 is typically connected to the center tap of a designated bridge branch 12 via a choke. Each bridge branch 12 selectively connects the current from the corresponding phase contact to either a lower contact 31 or an upper contact 32 of converter circuit 1. These contacts are connected via an intermediate circuit capacitor 33 and supply power to a DC-DC converter 4, and thus to a battery 5. The internal structure of converter circuit 1 and DC-DC converter 4 is not critical for implementation. Converter circuit 1 only needs to be able to set the current flowing through phase contacts 11. In particular, using a controller, it can set the sinusoidal curve of each current, with both the amplitude and phase shift being adjustable.

[0043] Figure 2 A converter circuit is shown with a designated controller 2. The controller comprises a gate signal generator 23 which

[0044] • Receives the amplitude and phase shift of the input phase currents I1, I2, I3 as set values ​​as control input signals;

[0045] • receiving the measured phase currents I1a, I2a, I3a and the phase voltages V1, V2, V3 as measured values;

[0046] • Outputs a gate signal 24 to the converter circuit 1 as a command signal.

[0047] The setpoints are determined by preprocessing stage 21, which receives the current limit values ​​I1d, I2d, and I3d from current maximum value acquisition unit 20. In preprocessing stage 21, input phase current setpoints I1, I2, and I3 are determined based on these current limit values. From this, the setpoints for phase shifts φ1, φ2, and φ3 are determined in phase shift evaluation unit 22.

[0048] The current limits I1d, I2d, and I3d may be specified by the power distribution network and transmitted to the multiphase converter 10. A power distribution network that includes devices for detecting power consumption values, switching or controlling consumers, and transmitting data regarding power supply status is known as a smart grid. Such a smart grid can thereby transmit the maximum available power or maximum permitted current for each phase to the multiphase converter 10.

[0049] At least one static load, or one that dynamically changes by switching on, off, or continuously (hereinafter referred to as an external load), can be connected to one or more phases, also supplying power to the multiphase converter via these phases. The maximum current currently available to the multiphase converter is limited by this external load. For example, for an 11 kW charger, the current in one phase can be limited to 10 A, while the current in the other phases is unrestricted, meaning that a nominal phase current of 16 A is available in the other phases. Smart grids can incorporate information about the status of the external load into the current limits I1d, I2d, and I3d.

[0050] Passes preprocessing level 21 check:

[0051] • Are the current limits I1d, I2d, and I3d achievable? For example, the combination of I3d = 16A, I1d = I2d = 6A is not achievable.

[0052] • If this is not possible, what are the current amplitudes I1, I2, and I3 that achieve maximum charging power for the input phase current settings? In the example above, these values ​​are I3 = 10.4A and I1 = I2 = 6A. Here, .

[0053] The phase shift evaluation unit 22 is Figure 3 Phase shifts φ1, φ2, and φ3 are determined in the following manner as shown. The figure shows the voltages and currents at the input terminals of converter circuit 1. From the perspective of phase contact 11, converter circuit 1 can be equivalent to a triangular circuit of resistors. The figure shows a combination of phasor diagrams for the voltages V1, V2, and V3 at phase contact 11 and the phase currents I1, I2, and I3 flowing into phase contact 11 (vector variables are generally shown in bold). Virtual triangular currents flow in the equivalent circuit with a phase shift of 120° relative to each other and amplitudes J1, J2, and J3. The triangular currents are vectorially added at the contacts of the equivalent circuit to form the incoming currents (phase currents). Since there is no zero conductor, the vector sum of the incoming currents should be zero. Based on this condition and the vector sum, the following equations can be derived to determine the phase shifts φ1, φ2, and φ3 of the phase currents for given amplitudes I1, I2, and I3. By applying the cosine law, these equations are:

[0054] ,

[0055] ,

[0056] .

[0057] These equations can usually be solved using numerical approximations based on the magnitudes of the triangular currents J1, J2, and J3. In rare cases, such as when the currents in both phases are equal, analytical solutions can be obtained. This occurs when the external load is connected to only one of the phases.

[0058] like Figure 3 As shown, for the amplitudes of the triangle current J1, J2, and J3, Figure 3 Applying the cosine law to the triangular current in the input phase current setting value can obtain the phase shift:

[0059] ,

[0060] ,

[0061] .

[0062] If it is assumed that the phase shift of the current relative to the voltage is in the range of +30° to -30°, and the maximum current amplitude is, for example, according to If we restrict , the solution is clear.

[0063] Mathematically equivalent methods can be performed that produce the same results when implemented in practice. For example, the values ​​can be normalized to one of the current magnitudes when calculating.

[0064] If certain operating conditions are known in advance, the solutions to the equations can be precomputed and stored in the controller and recalled when such operating conditions occur. This can be achieved, for example, if the external load has only a finite number of load levels, such as a boiler that turns on and off.

[0065] Therefore, starting from the specified current limits I1d, I2d, and I3d, and if necessary reducing the maximum current amplitude, a physically achievable solution for the phase shift of the three currents exists, in which the current complements are zero. This results in the current amplitudes for the input phase current setpoints I1, I2, and I3. The setpoints for the phase shifts φ1, φ2, and φ3 of the phase currents are thus determined by the virtual triangular current amplitudes. The gate signal generator 23 uses these setpoints for closed-loop control of the converter circuit 1. This achieves the maximum power consumption of the converter circuit 1. The power consumption 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, in turn, is the product of the voltage at each phase contact 11 and the current multiplied by the cosine of its phase shift.

[0066] Figure 4 shows a three-phase supply with specified loads between the phases and the star point, and Figure 5The figure shows the current in a power supply when controlling a three-phase converter for maximum power consumption. For example, consider a 230V / 400V three-phase power supply. A uniform power load of 16 A per phase is achieved. The converter achieves a maximum power output of 9.5 kW. Here, the load on one phase is reduced due to the additional external load on the neutral line.

[0067] As an alternative to maximizing power dissipation, the phase currents can be selected to minimize ripple at the input of converter circuit 1. To this end, the three input phase current setpoints I1, I2, and I3 are set equal to one another and to the minimum of the three current limits I1d, I2d, and I3d. This keeps the fluctuation of absorbed power within the full wave ("power ripple") as small as possible.

[0068] Figure 6 shows the same three-phase power supply, and Figure 7 The currents in the power supply are shown when the three-phase converter is controlled to achieve power balance at the converter. This results in uniform device loading of the converter. Assuming equal loading on all three phases at the device input, the maximum possible power is 6.9 kW; in this case, all three phases draw current from the least loaded phase.

[0069] In some embodiments, an intermediate solution between maximum power consumption and uniform device loading of the converter can be achieved. For example, if the required power is less than the maximum possible power, the "best balance" can be considered the operating point that achieves the minimum power ripple. For example, if the power is limited to 6 kW, one phase current is limited to 10 A, and the other two phase currents are limited to 16 A. Then, one phase can be loaded with 10 A, and the other two phases with approximately 7.5 A, thus generating power ripple; alternatively, all three phases can be loaded with 8.7 A, achieving symmetrical loading and thus generating ripple-free power.

[0070] Alternatively, a closed-loop control can be performed to make the load of the power supply (not shown) at least approximately uniform. To this end, information about the load caused by the asymmetrical load must be available.

Claims

1. A multiphase converter (10) for phase load balancing, comprising a converter circuit (1) and a controller (2), in, The converter circuit (1) comprises three or more phase contacts (11) and is designed to supply power to an electrical device. The controller (2) is designed to control the converter circuit (1) and thereby perform closed-loop control on a specified input phase current in each of the three phase contacts (11) to achieve predetermined input phase current set values ​​I1, I2, I3, It is characterized in that The controller (2) is designed to determine the input phase current set values ​​I1, I2, I3 as vector variables when the converter circuit is operating, each vector variable having a current amplitude I1, I2, I3 and a phase shift φ1, φ2, φ3, such that • the current amplitudes of the input phase current setting values ​​I1, I2, I3 are respectively less than or equal to the specified maximum current amplitudes I1d, I2d, I3d, the maximum current amplitudes I1d, I2d, I3d hereinafter also referred to as current limits; • the power flowing into the converter circuit (1) at the phase contacts (11) is maximized; • and, optionally, satisfying specified constraints on the phase shift of the input phase currents.

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

3. The multiphase converter (10) for phase load balancing according to claim 1 or 2, wherein: The controller is designed to determine in a verification step whether the current amplitudes of the input phase current set values ​​I1, I2, I3 can be achieved, wherein these current amplitudes are equal to the specified current limits I1d, I2d, I3d, respectively, and Otherwise, the maximum current amplitude among the current limits is reduced.

4. The multiphase converter (10) for phase load balancing according to claim 1 or 2, wherein: The controller is designed to determine the current amplitudes of the input phase current setpoints I1, I2, I3 based on the virtual triangle current amplitudes J1, J2, J3, wherein the following formula applies: ， ， 。 5. The multiphase converter (10) for phase load balancing according to claim 4, wherein: The controller is designed to determine the phase shift of the input phase current setpoint as: ， ， 。 6. A multiphase converter (10) according to any one of the preceding claims, designed for closed-loop control of the converter circuit (1) to achieve maximum power dissipation at the phase contacts (11), subject to the constraint that the current amplitudes of the input phase current setpoints I1, I2, I3 are equal.

7. The multiphase converter (10) according to any one of the preceding claims, wherein The controller (2) is configured to store or receive load limit information about at least one phase contact (11), and reduce the current limit value of the phase contact (11) according to the load limit information.

8. A method for operating a multiphase converter (10) for phase load balancing, the multiphase converter (10) comprising a converter circuit (1) and a controller (2), in, The converter circuit (1) comprises three or more phase contacts (11) and is designed to supply power to an electrical device. The controller (2) controls the converter circuit (1) and thereby performs closed-loop control on a specified input phase current in each of the three phase contacts (11) to achieve predetermined input phase current set values ​​I1, I2, I3, Its characteristics are: The controller (2) determines the input phase current set values ​​I1, I2, I3 as vector variables, each vector variable having a current amplitude I1, I2, I3 and a phase shift φ1, φ2, φ3, such that • the current amplitudes of the input phase current setting values ​​I1, I2, I3 are respectively less than or equal to the specified maximum current amplitudes I1d, I2d, I3d, the maximum current amplitudes I1d, I2d, I3d hereinafter also referred to as current limits; • the power flowing into the converter circuit (1) at the phase contacts (11) is maximized; • and, optionally, satisfying specified constraints on the phase shift of the input phase currents.

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