Multiphase converter and method for compensating for phase loads

Abstract

A multiphase converter (10) for compensating for phase loads has a converter circuit (1) with phase connections (11) and controls a respective input phase current in each of the three phase connections (11) to a specified input phase current target value I1, I2, I3. In the process, the input phase current target values I1, I2, I3 are ascertained as vectorial variables, each of which has a current value I1, I2, I3 and a phase offset φ1, φ2, φ3, such that • the current values of the input phase current target values I1, I2, I3 are less than or equal to a respective maximum current value I1d, I2d, I3d, hereafter also referred to as current threshold value; • power flowing into the converter circuit (1) at the phase connections (11) is maximized; and • optionally, specified boundary conditions are maintained for the phase offsets of the input phase currents.

Description

[0001] MULTI-PHASE CONVERTER AND METHOD FOR

[0002] PHASE LOAD BALANCING

[0003] The invention relates to the field of electronic power converters. It relates to a multiphase converter for phase load balancing and a method for phase load balancing according to the preamble of the corresponding independent patent claims.

[0004] On-board chargers for electric vehicles (called "on-board chargers" or OBCs) can be connected to a three-phase network if a suitable network is available. Ideally, the power demand on each network phase is balanced, meaning that all phase currents supplied to the charger are equal. For example, a 1-liter truck charger for an electric vehicle draws 16 A per phase from a network with three 230 V nominal voltages, which is sufficient for a full charge overnight.

[0005] However, the load capacity of one or more phases may be limited under certain circumstances, for example due to another high load, such as a hot water boiler, an air conditioner, etc. If, for example, the maximum current per phase is 20 A and a hot water boiler draws 10 A from a phase at night, then the charger must reduce the power on that phase to 10 A or less. This can be achieved by a three-phase charger consisting of three single-phase chargers, each connected as a load between the phase and neutral conductors. Each of the three single-phase chargers can implement a power factor correction (PFC) circuit to comply with regulations for limiting the harmonics of the respective phase current. The three-phase charger therefore has three PFCs, each between the phase and neutral conductors.

[0006] WO 2018 / 176184 describes a voltage sensing circuit in a three-phase P CF network.

[0007] US Patent No. 8,788,106 B2 describes the distribution of electrical power to several aircraft wing de-icing devices according to the power requirements of each device. The devices are resistive heating elements in a three-phase electrical system. One constraint for the operation of the devices is to keep the neutral conductor current below a certain limit.

[0008] EP 3 435 533 A1 describes a three-phase electrical system with individual AC-DC phase modules in an AC-side star configuration. A method for regulating the voltage at the star point is disclosed. A similar method is also described in AU 2015203405 A1.

[0009] The object of the invention is to provide a multi-phase converter for phase load compensation and a method for phase load compensation of the type mentioned above, which has a lower circuit complexity with regard to the power components compared to existing solutions.

[0010] This problem is solved by a multi-phase converter for phase load compensation and a method for phase load compensation with the features of the corresponding independent patent claims.

[0011] The multi-phase converter serves for phase load balancing. It comprises a converter circuit and a controller, wherein the converter circuit has three or more phase connections and is designed to supply a load. The controller is designed to control the converter circuit and thereby regulate an assigned input phase current in each of the three phase connections to a predetermined input phase current setpoint II, I2, I3.

[0012] The control is designed to determine the input phase current setpoints II, 12, 13, as vectorial variables, each with a current value II, 12, 13, and a phase shift cp 1 , cp2, q>3, during operation of the converter circuit, such that

[0013] • the current values ​​of the input phase current setpoints II, I2, I3 are each less than or equal to an assigned maximum current value I Id, I2d, I3d, hereinafter also referred to as the current limit value;

[0014] • the power flowing into the converter circuit at the phase connections is maximized;

[0015] • and, optionally, specified boundary conditions for the phase shifts of the input phase currents are observed.

[0016] The converter circuit is described here and below as having three phase connections. However, it can also be implemented with more than three phase connections, in particular with six.

[0017] The load can be fed via a lower connection point and an upper connection point. The load can be fed if the converter circuit is designed to conduct currents from each of the three phase connections optionally to the lower or the upper connection point. In particular, the converter circuit can be set up to connect each of the three phase connections to a lower connection point or an upper connection point of a load. The fact that the controller is designed to determine the input phase current setpoints as vector variables, each with a current magnitude and a phase shift, means that the input currents are sinusoidal and form a three-phase system or a system with more than three phases.

[0018] With this multiphase converter, it is possible to form the input currents in such a way that they form a balanced system with three or more phases, which does not require a compensating current through a neutral conductor. In particular, however, there is no real neutral point in the converter circuit. Therefore, known approaches for controlling the converter circuit are not applicable.

[0019] The cost and size of the EV charger can be reduced by using a three-phase charger that does not require a neutral wire connection. For example, a three-phase inverter can be used as a PFC, and in the manner described here, the inverter can be controlled to create, for example, an unbalanced load that compensates for an existing, given load on the grid.

[0020] Since there is no neutral conductor, the possibilities for asymmetrical phase loading with a three-phase PFC are severely limited. With the described multiphase converter, a defined power can be drawn from the three-phase network within this limited framework, taking into account individual limits for all three phase currents. This can be the maximum available power. If not, then a degree of freedom remains to achieve the required power with the most balanced phase load possible. These limits can result from the load on the phases by other consumers.

[0021] To connect one of the input terminals optionally to a lower connection point or an upper connection point of a load, a half-bridge branch can be provided, assigned to the respective input terminal. A half-bridge branch can have a lower switch and a lower freewheeling diode connected between a center tap of the half-bridge branch and the lower connection point, as well as an upper switch and an upper freewheeling diode connected between the center tap of the half-bridge branch and the upper connection point. The center tap can be connected to the corresponding input terminal via a smoothing inductance.

[0022] In embodiments, the three or more phase terminals form primary-side terminals for supplying the multi-phase converter, and the multi-phase converter has no primary-side terminal for a neutral conductor.

[0023] In embodiments, the controller is designed to determine in a verification step whether current amounts of the input phase current setpoints II, I2, I3 can be realized which are each equal to the associated current limit value Ild, I2d, I3d, and otherwise reduce the current amount whose current limit value is the largest of the current limit values.

[0024] In a three-phase system, the verification step and any adjustment to be made can be realized by setting II = Ild and I2 = I2d, assuming that the largest maximum current is designated I3d, and I3 = min(j3d; V / l 2 + / I ■ / 2 + / 2 2 ). The verification step therefore corresponds to a check whether I3d is smaller than the root expression.

[0025] In embodiments, the controller is designed to determine the current magnitudes of the input phase current setpoints II, I2, I3 based on fictitious delta current magnitudes J1, J2, J3, wherein the following equations apply

[0026] / l 2 = ;i2 + J22 +J1 .J2 ,

[0027] I2 2 = J2 2 + J3 2 + J2 -J3 ,

[0028] The maximum possible power due to the limited phase currents is clearly defined as the solution to this system of equations. The three input phase current setpoints II, I2, I3 are specified, and the fictitious delta current values ​​J1, J2, J3 are to be determined. The solution is particularly clear if it is assumed that the phase shifts of the currents relative to the voltages are in the range +30° to -30°, and if the largest current value according to I3 = is limited.

[0029] If the required power is less than the maximum possible power, an operating point can be selected that results in the smallest power ripple.

[0030] In embodiments, the multi-phase converter is designed to regulate the converter circuit to maximum power consumption at the phase connections, with the boundary condition that the current values ​​of the input phase current setpoints are equal.

[0031] In embodiments, the controller is configured to store or receive load limiting information for at least one of the phase connections and to reduce the current limit value of this phase connection in accordance with this load limiting information.

[0032] Further preferred embodiments emerge from the dependent patent claims. Features of the method claims can be combined mutatis mutandis with the device claims, and vice versa.

[0033] The subject matter of the invention is explained in more detail below using preferred embodiments, which are illustrated in the accompanying drawings. They show schematically: Figure 1 shows a charger with a three-phase converter without a neutral point; Figure 2 shows the three-phase converter with an associated controller;

[0034] Figure 3 Voltages and currents at phase terminals of the three-phase inverter;

[0035] Figure 4 shows a three-phase network with a given load between a phase and a neutral point;

[0036] Figure 5 Currents in this network when the three-phase converter is optimized for maximum power consumption;

[0037] Figure 6 shows a three-phase network with a given load between a phase and a neutral point; and

[0038] Figure 7 Currents in this network when the three-phase converter is optimized for balanced supply currents.

[0039] In principle, identical or similarly functioning parts in the figures are provided with the same reference symbols.

[0040] Figure 1 shows a charger with a three-phase converter without a neutral point, hereinafter referred to as converter circuit 1. The converter circuit 1 has an input side or mains side with three phase connections 11. Each of the phase connections 11 leads, typically via a choke, to a center tap of an associated bridge arm 12. Each bridge arm 12 switches a current from the respective phase connection either to a lower connection point 31 or upper connection point 32 of the converter circuit 1. These connection points 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 the converter circuit 1 and the DC-DC converter 4 is not critical for implementation. The converter circuit 1 only needs to be at least capable of adjusting the currents flowing through the phase connections 11.In particular, it is capable of setting a sinusoidal waveform of each of the currents with a predeterminable amplitude and a phase shift by means of a controller 2.

[0041] Figure 2 shows the converter circuit with an associated control 2. This has a gate signal generation 23, which

[0042] • receives the amplitudes and phase shifts of the input phase currents II, 12, 13 as setpoints as control input signals,

[0043] • receives measured phase currents Ila, I2a, I3a and phase voltages VI, V2, V3 as measured values, and

[0044] • outputs gate signals 24 to the converter circuit 1 as manipulated variables.

[0045] The setpoints are determined by a preprocessing stage 21, which receives 20 current limit values ​​II d, I2d, I3d from a unit for maximum current value detection. From these current limit values, the input phase current setpoints II, I2, I3 are determined in a preprocessing stage 21. From these, the setpoints for the phase shifts cpl, cp2, <p3 ermittelt.

[0046] The current limit values ​​I1d, I2d, I3d can be specified by the supplying electrical distribution grid and transmitted to the multiphase converter 10. Electrical distribution grids with means for recording consumption values, switching or controlling loads, and transmitting data on the grid status are known as "smart grids." Such a "smart grid" can thus transmit the maximum available power or the maximum permissible current per phase to the multiphase converter 10.

[0047] At least one static or dynamically switched-on or continuously varying load, hereinafter referred to as the external load, can be connected to one or more of the phases that also supply the multiphase converter. This external load limits the maximum current still available to the multiphase converter. For example, for a 1 kW charger, one of the phase currents can be limited to 10 A, while the others are not, meaning that a nominal phase current of 16 A can be drawn from the other phase. Information about the state of the external load can be converted by the smart grid into the current limit values ​​Ild, I2d, and I3d.

[0048] Preprocessing stage 21 checks:

[0049] • Are the current limit values ​​Ild, I2d, and I3d feasible? For example, the combination I3d = 16A, Ild = I2d = 6A is not feasible.

[0050] • If they are not feasible, what are the feasible current values ​​II, I2, I3 for the input phase current setpoints that result in maximum charging power? In the example given, these are I3 = 10.4A, II = I2 = 6A.

[0051] The phase shift determination 22 determines the phase shifts cpl, <p2, cp3 in der folgenden Weise, anhand von Figur 3 erklärt. Diese zeigt Spannungen und Ströme an Eingangsklemmen der Umrichterschaltung 1. Von den Phasenanschlüssen 11 her betrachtet kann die Umrichterschaltung 1 durch eine Dreieckschaltung von Widerständen ersetzt werden. Die Figur zeigt eine Kombination der Zeigerdiagramme der Spannungen VI, V2, V3 an den Phasenanschlüssen 11 und der in die Phasenanschlüsse 11 hineinfliessenden Phasenströme II, 12, 13 (konventionsgemäss werden vektorielle Grössen fett gedruckt). In der Ersatz Schaltung fliessen fiktive Dreieckströme, mit einer gegenseitigen Phasenverschiebung von 120° und mit den Beträgen Jl, J2, J3. An den Anschlusspunkten der Ersatzschaltung summieren sich die Dreieckströme vektoriell zu den hineinfliessenden Strömen (Phasenströme). Die vektorielle Summe der hineinfliessenden Ströme soll Null sein, da kein Nullleiter vorhanden ist.From this condition and the vector sums, equations result from which the phase shifts cpl, cp2, cp3 of the phase currents are determined for a given magnitude II, I2, I3 of the phase currents. Applying the cosine theorem, these equations are:

[0052] These equations can generally be solved using a numerical approximation method for the magnitudes J1, J2, J3 of the delta currents. In individual cases, for example, when two of the phase currents are equal, analytical solutions are possible. This is the case when an external load is connected to only one of the phases.

[0053] With the amounts Jl, J2, J3 of the triangular currents, the phase shifts of the input phase current setpoints are obtained by applying the cosine theorem to the current triangles in Figure 3 as

[0054] The solutions are clear if it is assumed that the phase shifts of the currents relative to the voltages are in the range +30° to -30°, and if the largest current value is, for example, according to 13 — is limited.

[0055] Mathematically equivalent procedures can be used that, when implemented in reality, lead to the same result. For example, the values ​​can be normalized to one of the current values ​​during the calculation.

[0056] If certain operating situations are known in advance, the solutions to the equations can be calculated in advance and stored in the control system, and then retrieved when such an operating situation occurs. This can be the case, for example, with an external load that has only a limited number of load steps, such as a boiler that is switched on and off.

[0057] In summary, starting from the specified current limit values ​​I Id, I2d, I3d, the highest current amount is reduced if necessary, so that a physically feasible solution for the phase shifts of the three currents exists, with which the currents add up to zero. This results in the current amounts of the input phase current setpoints I1, I2, I3. From this, the setpoints for the phase shifts cpl, cp2, q>3 of the phase currents are determined, for example using the fictitious delta current amounts. These are used by the gate signal generator 23 to control the converter circuit 1. As a result, a maximum power consumption of the converter circuit 1 is achieved. The power consumption can be calculated in a known manner as the sum of the power flowing into the converter circuit 1 at each phase connection 11. This, in turn, is the product of the voltage and the current at the phase connection 11, multiplied by the cosine of their phase shift.

[0058] Figure 4 shows a three-phase network with a specified load between a phase and a neutral point, and Figure 5 shows the currents in this network when the three-phase inverter is driven to maximum power consumption. The example is a 230V / 400V three-phase network. A uniform network load of 16A per phase is achieved. The inverter draws a maximum possible network power of 9.5kW. One phase can only handle a reduced load due to an additional external load opposite the neutral conductor.

[0059] As an alternative to the maximum power consumption, the phase currents can be selected to minimize ripple at the input of converter circuit 1. To do this, the three input phase current setpoints I1, I2, and I3 are set equal to each other and to the smallest of the three current limit values ​​I1d, I2d, and I3d. The fluctuation in the absorbed power over a full wave ("power ripple Ii") is thus kept as small as possible.

[0060] Figure 6 shows the same three-phase network, and Figure 7 shows the currents in this network when the three-phase inverter is controlled to a balanced power level. This ensures a balanced load across the inverter. The maximum possible power is 6.9 kW with an identical load across all three phases at the device input; in this case, all three phases draw the current from the least loaded phase.

[0061] In some embodiments, an intermediate solution can be realized regarding the maximum power consumption and the uniform device load of the converter. For example, if the required power is less than the maximum possible power, a "best balance" can be considered the operating point that results in the smallest power ripple. For example, the power is limited to 6 kW, one phase current to 10 A, and the other two to 16 A. Then, one phase can be loaded with 10 A and the other two with approximately 7.5 A, creating a power ripple, or all three phases can be loaded with 8.7 A, resulting in a symmetrical load and thus ripple-free power.

[0062] Alternatively, the load on the supply network can be regulated to at least be approximately uniform (not shown). For this, information about the load caused by the asymmetric load must be available.

Claims

PATENT CLAIMS 1. Multi-phase converter (10) for phase load compensation, comprising a converter circuit (1) and a controller (2), wherein the converter circuit (1) has three or more phase connections (11) and is designed to feed a consumer, wherein the controller (2) is designed to control the converter circuit (1) and thereby regulate an assigned input phase current in each of the three phase connections (11) to a predetermined input phase current setpoint II, I2, I3, characterized in that the controller (2) is designed to, during operation of the converter circuit, the input phase current setpoints II, I2, I3 as vectorial variables, each with a current amount II, I2, I3, and a phase shift epi, <p2, <p3, derart zu ermitteln, dass • the current values ​​of the input phase current setpoints II, I2, I3 are each less than or equal to an assigned maximum current value I1d, I2d, I3d, hereinafter also referred to as the current limit value; • a power flowing into the converter circuit (1) at the phase connections (11) is maximized; • and, optionally, specified boundary conditions for the phase shifts of the input phase currents are observed.

2. Multi-phase converter (10) according to claim 1, wherein the three or more phase terminals (11) form primary-side terminals for supplying the multi-phase converter (10), and the multi-phase converter (10) has no primary-side terminal for a neutral conductor.

3. Multi-phase converter (10) for phase load compensation according to claim 1 or 2, wherein the controller is designed to, in a verification step, determine whether current amounts of the input phase current setpoints II, I2, I3 can be realized which are each equal to the assigned current limit value Ild, I2d, I3d, and otherwise reduce the current amount whose current limit value is the largest of the current limit values.

4. Multi-phase converter (10) for phase load compensation according to claim 1 or 2, wherein the controller is designed to determine the current amounts of the input phase current setpoints II, I2, I3 based on fictitious delta current amounts Jl J2 J3, wherein the following equations apply 5. Multi-phase converter (10) for phase load compensation according to claim 4, wherein the controller is configured to determine the phase shifts of the input phase current setpoints as 6. Multi-phase converter (10) according to one of the preceding claims, designed to regulate the converter circuit (1) to maximum power consumption at the phase terminals (11), with the boundary condition that the current values ​​of the input phase current setpoints II, I2, I3 are equal.

7. Multi-phase converter (10) according to one of the preceding claims, wherein the controller (2) is configured to store or receive load limiting information for at least one of the phase terminals (11) and to reduce the current limit value of this phase terminal (11) in accordance with this load limiting information. 8 Method for operating a multi-phase converter (10) for phase load compensation, comprising a converter circuit (1) and a controller (2), wherein the converter circuit (1) has three or more phase connections (11) and is designed to feed a consumer, wherein the controller (2) controls the converter circuit (1) and thereby regulates an assigned input phase current in each of the three phase connections (11) to a predetermined input phase current setpoint II, 12, 13, characterized in that the controller (2) the input phase current setpoints II, 12, 13, as vectorial variables each with a current amount II, 12, 13, and a phase shift cpl , cp2, <p3, derart ermittelt, dass• the current values ​​of the input phase current setpoints II, I2, I3 are each less than or equal to an assigned maximum current value II d, I2d, I3d, hereinafter also referred to as the current limit value; • a power flowing into the converter circuit (1) at the phase connections (11) is maximized; • and, optionally, specified boundary conditions for the phase shifts of the input phase currents are observed.

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