Power electronics converter system having a plurality of converter units for providing a common output voltage, and method for operating same

Abstract

The invention relates to a converter system (1) having a plurality of converter units (2) which are connected in parallel on the output side and together provide an output voltage (ULV) for operating a load, wherein each of the converter units (2) comprises: - a power electronics converter device (23), which is designed to provide a current contribution for operating the load depending on a predefined partial target current (IL,1 ref,,iL,2, ref,iL,3, ref); - a voltage measuring unit (22) for detecting the output voltage (ULV); - a voltage regulation block (21), which is designed to regulate the output voltage (ULV) to a predefined target output voltage by providing a target current (iL ref); and - a division block (49), which is designed to provide the partial target current (IL,1, ref,iL,2, ref,iL,3, ref) for the converter device (23) depending on a correspondingly predefined division factor (F1, F2, F3) and the target current (iL ref).

Description

[0001] R.410698 - 1 -Description Title Power electronic converter system with multiple converter units for providing a common output voltage and method for its operation Technical field The invention relates to converter systems in which several converter units, for example DC / DC or AC / DC converters, are connected in parallel on the output side to jointly provide an output voltage for operating a load. The invention further relates to the implementation of a distribution between the converter units, particularly when these are to supply varying load contributions. Technical background Converter systems for providing an output voltage for loads with high power consumption can be implemented with several converter units that are connected in parallel on the output side. These converter units can have an identical or different circuit design and have different contributions to supplying the connected load.Such converter systems typically feature a master control unit that determines the total load current from the voltage difference between a setpoint voltage and the output voltage. A current distribution block specifies setpoint currents for the individual converter units, which are then implemented via corresponding current controls within the converter units. The partial currents are then added together at the output to operate the required load. R.410698 -. 2 -Generally, the desired distribution is achieved based on a master-slave operation, where voltage regulation is performed jointly and the target current is divided according to a predefined distribution. The resulting partial target currents are then transmitted to the converter units via a high-speed communication link. This communication link is part of the control system and therefore significantly limits the control frequency. However, the implementation of this control structure requires a high-speed communication link that operates in real time with minimal delay, as it is an integral part of the control system. If the communication leads to significant delays, as is often the case in practice, the control structure can only implement voltage regulation with very low bandwidth. This is disadvantageous for rapid compensation of load changes.In distributed systems, bus systems are frequently used to communicate the partial set currents, leading to significant delays typically exceeding 500 µs, which is common for communication systems such as CAM. The limited bandwidth of this type of control makes it difficult to quickly compensate for load changes, as required in many applications. Alternative approaches, known as droop control, involve equipping each converter unit with its own voltage regulator, which simulates the behavior of an internal resistance at the output terminal. Such regulators then set an output voltage that remains within a defined range depending on the current flow. This distributes the power among the individual converter units according to their internal resistance ratios. With this approach, no communication is necessary.However, steady-state regulation of the output voltage cannot be performed. Such regulation can be achieved via a higher-level control loop, which changes the output voltage level via the communication interface. However, this regulation can only be performed very slowly, as otherwise resonances will occur between the droop control system and the cascaded control system. R.410698 -. 3 -A fundamental problem with prior art approaches is the lack of converter systems capable of regulating an output voltage with rapid dynamics and steady-state accuracy under varying loads, provided there is no high-speed communication link between the converter units. The object of the present invention is to provide a converter system with multiple converter units in which several units can jointly operate a variable load and a variable distribution between the converter units with high bandwidth is possible. Furthermore, it is desirable to ensure highly dynamic operation with the best possible distribution even when there is an error in the data transmission of the partial setpoint currents via the communication link.Disclosure of the invention: According to the invention, a converter system with multiple converter units for providing an output voltage for operating a load with varying power requirements according to claim 1, and a method for operating such a converter system according to the dependent claim, are provided. Further embodiments are specified in the dependent claims.According to a first aspect, a converter system with several converter units is provided, which are connected in parallel on the output side and together provide an output voltage for operating a load, wherein each of the converter units comprises: - a power electronic converter device configured to provide a current contribution for operating the load depending on a predetermined partial set current; - a voltage measuring unit for sensing the output voltage; - a voltage regulation block configured to adjust the output voltage to a predetermined set output voltage by R.410698 -. 4 -To regulate the provision of a target current; - a distribution block designed to provide the partial target current for the converter unit, depending on a correspondingly predefined distribution factor and the target current. The converter system has several converter units, each cascaded and controlled, so that a higher-level voltage control exists which provides a target current as a manipulated variable, depending on a target output voltage. Using the distribution factor, a partial target current is provided for a downstream current control of each of the converter units of the respective converter unit. The converter units are connected in parallel on the output side and can be connected in series or parallel on the input side. The converter units can also be of different or the same type. For example, AC / DC converters or DC / DC converters can be used together as converter units.To operate a load with varying power consumption and to provide a fixed or variable distribution between the individual converter units, a highly dynamic control system is necessary to meet the demands of rapidly varying power consumption by the load. As described above, the dynamics of the control systems can be significantly limited, especially in distributed systems, if the communication of the distribution of the partial setpoint currents or similar is part of the control loop. The voltage control block can include a voltage control that has at least an integrator component on which the setpoint current depends, wherein the integrator component is, in particular, equipped with an anti-windup function. The control system of the converter system can provide a separate, in particular identical, voltage control for each of the converter units, which can, in particular, have a proportional component and an integrator component.The voltage regulators preferably use the identical control function and should thus, under ideal conditions, i.e., with the same voltage measurement of the output voltage and the same target output voltage, the R.410698 -. 5 -The system outputs an identical control variable of a target current. This control variable is used as the target current with which the output-side buffer capacitor is to be charged or the capacitor voltage is to be kept as constant as possible at the target voltage level. The resulting control variable of the target current is multiplied by a distribution factor that indicates the contribution of the corresponding converter unit to the output power to be provided. Using this distribution, a partial target current is determined for each converter unit as a portion of the total current to be provided, which the respective converter unit is to contribute. This allows for the distribution of the output currents across all converter units in order to take into account the requirements of the converter units or, if necessary, a power limit of individual converter units. The distribution of the target current can be transmitted via the communication link between the converter units.However, the current control is implemented independently in each of the converter units. The converter system according to the invention therefore provides for the individual converter units to be equipped with separate voltage controls, which are further controlled by a distribution provided by a higher-level control system, so that the partial setpoint currents, as control variables of the voltage controls, are in a ratio to each other predetermined by the distribution. The distribution factor can be provided synchronously to the voltage controls, but is not part of the control loop and thus does not limit the dynamics of the control in the case of dynamically changing power requirements in the load. Under ideal boundary conditions, such an architecture of the converter system achieves a highly dynamic steady-state regulation of the output voltage and a desired distribution between the converter units.Since the converter units can also be arranged in a distributed manner, it is necessary that each voltage regulator has its own output voltage sensing system (i.e., the actual output voltage) with a corresponding voltage measuring unit. These voltage measuring units can have errors, especially offset errors as measurement offsets, so that the input-side R.410698 -. 6 -The voltage measurements provided by the voltage regulator are not necessarily identical, even with the same actual output voltage. Furthermore, the voltage measurement of the individual converter units takes place at different points in the output circuit, so that the actually measured voltages can also deviate slightly from one another due to line resistances. These measurement errors in the voltage values ​​have no significant effect on the proportional component of the voltage regulation, so they only lead to minor differences in the calculation of the proportional state feedback of all units.However, the measurement errors in the voltage readings significantly affect the integrator component of the individual converter units. Even the slightest measurement offsets of the voltage measuring units cause the deviations of the voltage readings from a predefined target output voltage to be integrated, so that the integrator components of the individual voltage regulators of the converter units can diverge considerably after a few control cycles. Therefore, the integrator components are provided with an anti-windup, thus limiting the integrator components of the voltage regulators. This can lead to some converter units operating at maximum current within the current limit of the integrator's anti-windup, while other voltage regulators exhibit zero current, and only one converter unit operates in the linear region of the voltage regulation. This significantly complicates the use of the converter system architecture described above.This problem can be circumvented by synchronizing the integrator components with each other. To achieve this, the integrator components are updated, particularly at a frequency significantly lower than the control frequency, by communicating their values ​​(i.e., the integrator counter values) to all other voltage regulators in the converter units. This allows each voltage regulator to manipulate the value of its own integrator component so that it approaches or is reset to the average value of all integrator components. Communicating the values ​​of the integrator components has the advantage that they can change much more slowly than the state variables of the converter system (i.e., the target output voltage and current, or R.410698). 7 -Power requirements. A low bandwidth communication link for transmitting the integrator component values ​​is therefore not a disadvantage. Furthermore, only the divergence of the integrator component values ​​is relevant for synchronization, which in turn occurs more slowly. For this reason, a communication interface between the voltage regulators of the converter units without real-time behavior, which can also exhibit larger delays, can be used for synchronizing the integrator value without restriction. Additionally, a balancing control can be implemented for each of the converter units to provide offset compensation depending on the difference between a value of the integrator component of the respective converter unit and an average value of the integrator component values ​​of all converter units.To avoid exciting oscillations in the individual voltage regulators, the values ​​of the integrator components should not change abruptly. Therefore, deviations in the values ​​of the integrator components can be compensated for using an offset correction, which corresponds to the measurement offset resulting from the differently measured output voltages. The measurement offsets are estimated and compensated for in such a way that the drift of the values ​​of the integrator components in the voltage regulators is counteracted. The offset correction can be implemented using a balancing regulator, which can also be implemented as a PI controller. This serves to compensate for a voltage offset resulting from the deviation of the value of the integrator component from an average value of the integrator components of the voltage regulators.This allows the calculated error of each converter unit to be used to calculate an offset compensation as a measurement offset, which compensates for the respective difference between the measured output voltage and the target output voltage, or the differences between the values ​​of the integrator components of the individual converter units and their mean value. This balancing control thus ensures that the integrator components of the individual R.410698 units are balanced. 8 -The converter units remain the same even if the measured output voltages yield different results. When calculating the error or deviation, it is important to note that these two values ​​are assigned to the same time step of the control system, and this time step must be delayed by a delay corresponding to the transmission latency of the communication link. For stability, the balancing controller must have a lower control frequency than the control frequency of the voltage control system. This ensures that the target current is distributed between the converter units in the desired ratio and that the voltage is regulated as accurately as possible. The steady-state voltage value corresponds to the control system's reference value plus the average of the measurement offsets. Thus, the output voltage is regulated without steady-state errors when the measurement offsets are average-free.If the mean measurement offset of the converter units deviates from zero, the voltage regulation of the converter system will always achieve a steady-state accuracy that is better than the accuracy of the voltage regulation of the worst-performing converter unit. In particular, a differential element can be provided that supplies a control deviation for the voltage regulation corresponding to the difference between a setpoint output voltage and an actual output voltage, whereby the differential element also receives the offset compensation to determine the control deviation depending on the offset compensation. Alternatively, another integrator unit can be provided to integrate the offset compensation, and a summing element can be provided to apply the setpoint current as the manipulated variable of the voltage regulation with the integrated offset compensation. The additional integrator unit can behave in the same way as the integrator of the voltage regulation.Thus, instead of estimating the measurement offset in the voltage control, the correction term of the synchronization control can be used by R.410698. 9 -A further integrator unit is integrated. The resulting value is added to the output of the voltage regulation. This means that the integrator component of the voltage regulation is not used as a second integration stage, but rather an independently implemented integrator unit in parallel. This dual integration stage, which is used in both implementations, enables the compensation of a linearly increasing deviation between the values ​​of the integrator components. Even if the communication of the integrator values ​​is interrupted or fails, the voltage regulation maintains the compensation in steady state, so that the load current can be distributed in the desired ratio.According to a further aspect, a method for operating the above converter system is provided, wherein a balancing control is carried out for each of the converter units to provide offset compensation depending on a difference between a value of the integrator component of the respective converter unit and an average value of the values ​​of the integrator components of all converter units, wherein each of the converter units communicates a value of the integrator component to all other converter units. Brief description of the drawings: Embodiments are explained in more detail below with reference to the accompanying drawings. They show: Figure 1 a block diagram of a converter system with several converter units, each operated via a separate voltage control; Figure 2 an embodiment for implementing a voltage control for a converter unit in the converter system. Figur 1;Figure 3 Signal timing diagrams to illustrate an example R.410698 - 10 - to compensate for the load distribution on the converter units when different measurement offsets of the respective voltage measurement units are present; and Figure 4 shows a block diagram of another converter system according to a further embodiment. Description of embodiments Figure 1 shows a schematic block diagram of the structure of a converter system 1 according to an embodiment of the invention. Figure 1 shows a converter system 1 with three converter units 2, each of which provides an output current iL,1, iL,2, iL,3 to maintain an output capacitance CA at a specific output voltage ULV. The output voltage ULV is to be maintained by the converter units 2 at a predetermined target output voltage ULV. refThe converter units 2 are connected in parallel on the output side to jointly provide the output voltage ULV. On the input side, the converter units 2 can be connected in series, in parallel, or in combinations thereof. The converter units 2 are supplied via a voltage source. Each converter unit 2 comprises a voltage control block 21, which has its own voltage measuring unit 22 for measuring the applied actual output voltage, and a converter device 23 as the power component of the converter. The voltage control block 21 uses an output voltage ULV measured by the voltage measuring unit 22 to provide a set current for controlling the converter device 23. The converter units 2 can be any AC / DC converters or DC / DC converters and can also be of different types.Possible converter units 2 include phase-shifted full bridge, multi-phase buck converter, boost / bubble converter and boost converter, flow converter, SPIC and CUK converter, flyback converter, dual active bridge converter, resonant converter with synchronous rectification and with phase shift - R.410698 -. 11 - Full-bridge converters and single- or multi-phase PFC converters (2-level / Vienna / 3-level NPC or T-type or multilevel) are used. The converter units 2 can be arranged as a compact unit or remotely from one another in a distributed system. The converter units 2 are each operated by a controller or a current control 24, which converts a manipulated variable as a partial setpoint current IL,1ref,iL,2ref,iL,3ref into a corresponding control signal for the respective converter unit 23 in a manner known per se, in order to achieve a partial setpoint current I corresponding to the respective partial setpoint current I. L,1 ref ,i L,2 ref ,i L,3 refto provide the corresponding output current IL,1,iL,2,iL,3. The resulting output currents IL,1,iL,2,iL,3 charge the output capacitor CA, which is preferably regulated to a predetermined target output voltage ULV by the voltage regulation described below. refto be maintained. Thus, the sum of the current contributions of the output currents IL,1,iL,2,iL,3 of the individual converter units 2 corresponds to the load current iL, which corresponds to the power requirement of the connected load L. Figure 2 shows a more detailed representation of the voltage control block 21. The voltage control block 21 comprises a voltage regulator 41, which is configured as a PI controller. The PI controller includes a proportional component 42 with a proportional factor Kp,u, and an integral component 43 with an integrator factor Ki,u. The integrator component 43 of the voltage regulator 41 has an anti-windup function, i.e., the integrator component can be limited against ramping up in the positive or negative direction. The outputs of the proportional component 42 and the integral component 43 are added in a summing element 53 and the result is provided as the target current as the total current for operating the load.Furthermore, the voltage control block 21 has a communication interface 51 to communicate the value of the integrator component 43 to the other voltage control units either directly or via a communication unit. The communication interface 51 is also designed to receive the corresponding values ​​of the integrator components of the other voltage control units. This can be done using a bus system 4, which transmits the integrator components or integrator values ​​i. L,i_val1 , i L,i_val2, i L,i_val3 Each of its converter units 2 communicates with all the others. Furthermore, a distribution factor R.410698 can also be communicated via the bus system 4 and the communication interfaces 51. 12 -F1, F2, F3… are received, indicating what proportion of the power requirement of the connected load is to be provided by the respective converter unit 2. In a subsequent distribution block 49, a portion of the target current is supplied as the partial target current I according to the distribution factor F1, F2, F3, which is specified externally or fixed. L,1 ref ,i L,2 ref ,i L,3 ref for the subsequent current regulation or control of the corresponding converter device 23, so that the corresponding partial current I is present there L,1 ,i L,2 ,i L,3 to the output capacitor C A Furthermore, the output of the integral component iL,i_val1, iL,i_val2, iL,i_val3 is provided for transmission to the other converter units 2 of the converter system 1. On the input side of the voltage control 41, a control deviation between a target output voltage ULV is determined using a differential element 44. refand the output voltage ULV detected by the voltage measuring unit 22. The control deviation is compensated for by an offset compensation ^ ^^^^^^ actuated, which results from a balancing control 50. The balancing control 50 can also be designed as a PI control and provides the offset compensation as the manipulated variable ^. ^^^^^^The balancing control 50 is provided with a control deviation derived from the mean value ^^̅, ^^^^ of all values ​​of the integrator components of all voltage regulators of all converter units 2 and the current value of the integrator component of the voltage regulator 41 itself. The mean value ^ ̅^,^^^^ of the values ​​of the integrator components is determined in all voltage regulators in the summing block 46 and the division block 47. The control deviation is determined in a differential element 48 as the difference between the current value of the integrator component of its own voltage regulator and the mean value ^ ̅^,^^^^ of all values ​​of the integrator components and is fed to the balancing control 50. The balancing control 50 regulates a control deviation and represents R.410698 - 13 - a correction value, the offset compensation ^^^^^^^ , which is applied as a measurement offset to the control deviation between the measured output voltage ULV and the target output voltage ULV refis subjected to this. As a result, the voltage control takes the measurement offset into account, which counteracts the unchecked up-integration in the integrator component of the voltage control. Figure 3 shows the simulation results of the voltage control using signal-time diagrams. The load current iL,1, iL,2, iL,3 of the individual converter units 2 and the estimated measurement offset uoffset,1, uoffset,2, uoffset,3 during voltage measurement are shown. At the beginning of the simulation, the balancing control is deactivated, so that the first converter unit 2 carries the entire load current iL,1, while the other converter units 2 carry no current iL,2 = 0, iL,3 = 0. The first converter unit carries the entire load current because, due to the negative measurement offset, it achieves the maximum value of the integrator component and thus pushes the other converter units aside.The balancing control begins operating at t = 25 ms and adjusts the values ​​of the integrator components so that the total current of 150 A is provided equally by all transducer units 2. Simultaneously, the control correctly estimates the measurement offsets of the individual transducer units 2, preventing a further accumulation of deviations. At time t = 180 ms, a load step occurs from 150 A to 300 A. This load step is stabilized by the control with high dynamics, as the measurement offsets of the voltage measurements are correctly compensated. Figure 4 shows another embodiment in which the offset compensation does not address the control deviation between the measured output voltage ULV and the target output voltage ULV. refcorrected, but is first integrated in a further integrator unit 52 and the resulting value in the summing element 53 affects the control variable of the voltage control 41. Preferably, the further integrator unit 52 behaves in the same way as the integrator part 43 of the voltage control 41. The operating principles of this alternative implementation are almost identical to the embodiment of Fig. 1, except that instead of the integrator part 43 of the voltage control 41 being used as the second integration stage, an independently parallel integrator unit 52 is used. This double integration stage R.410698 - 14 - This can be used to implement the internal mode principle and to regulate the linearly increasing deviation.

Claims

R.410698 - 15 -Claims 1. Converter system (1) with several converter units (2) connected in parallel on the output side and jointly providing an output voltage (ULV) for operating a load, wherein each of the converter units (2) comprises: - a power electronic converter device (23) configured to provide a current contribution for operating the load depending on a predetermined partial set current (IL,1ref,iL,2ref,iL,3ref); - a voltage measuring unit (22) for detecting the output voltage (ULV); - a voltage regulation block (21) configured to regulate the output voltage (ULV) to a predetermined target output voltage by providing a target current (iLref); - a distribution block (49) configured to provide the partial target current (IL,1ref,iL,2ref,iL,3ref) for the converter device (23) depending on a correspondingly predetermined distribution factor (F1, F2, F3) and the target current (iLref).2.Converter system (1) according to claim 1, wherein the voltage control block (21) has a voltage control (41) which has at least one integrator component (43) from which the set current (iL. ref ) depends, wherein the integrator portion is in particular provided with an anti-windup.

3. Converter system (1) according to claim 2, wherein each of the converter units (2) is configured to measure the set current (i L ref ) as a control variable depending on the values ​​of the integrator components (iL,i_val1, iL,i_val2, iL,i_val3) of all converter units (2).

4. Converter system (1) according to claim 2 or 3, wherein a balancing control (50) is provided for each of the converter units (2) to correct an offset R.410698 - 16 - compensation depending on a difference between a value of the integrator component (iL,i_val1, iL,i_val2, iL,i_val3) of the voltage control (41) of the respective converter unit (2) and an average value (^ ̅^,^^^^) of the values ​​of the integrator components of the voltage controls (41) of all converter units (2).

5. Converter system (1) according to claim 3, wherein a differential element (44) is provided which provides a control deviation for the voltage control (41) corresponding to a difference between a target output voltage (ULVref) and an actual output voltage (ULV), wherein the differential element (44) further provides the offset compensation (^ ^^^^^^ ) receives, depending on the offset compensation (^ ^^^^^^ ) to determine the control deviation.

6. Converter system (1) according to claim 3, wherein a further integrator unit (52) is provided to integrate the offset compensation, and a summing element (53) is provided to determine the setpoint current (iL). ref) as a control variable of the voltage control (41) with the integrated offset compensation (iL,Δ).

7. Converter system (1) according to any one of claims 3 to 5, wherein the balancing control (50) has a lower control frequency than the voltage control (41).

8. Converter system (1) according to any one of claims 3 to 6, wherein the balancing control (50) has at least one integrator component.

9. Converter system (1) according to any one of claims 3 to 7, wherein a communication unit (51) and a bus system (4) are provided to communicate the value of the integrator component (iL,i_val1, iL,i_val2, iL,i_val3) for each of the converter units (2) to all other converter units (2).

10. Method for operating a converter system (1) according to one of claims 2 to 9, wherein a balancing control (50) is carried out for each of the converter units (2) in order to perform offset compensation ab-depending on a difference between a value of the integrator term (i L,i_val1 , i L,i_val2, i L,i_val3 ) of the relevant converter unit (2) and an average value (^ ̅^,^^^^) of the values ​​of the integrator components of all converter units (2) R.410698 - 17 - to provide, wherein each of the converter units (2) represents a value of the integrator component (i L,i_val1 , i L,i_val2, i L,i_val3 ) communicates to all other converter units (2).

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