Patent Application
20160126843
The present disclosure relates to a power system with adaptive control and a related method.
In DC-DC conversion it is often convenient to parallel power stages with a common output voltage in order to supply high currents to a load. In this way power conversion can be achieved with scalable and modular components. For example, in point of load (POL) module applications multiple POL modules can be employed in parallel to supply the required current to the load
Traditionally, current share is achieved between parallel converters be means of active or passive methods. In active methods a current share bus is employed between controllers. In passive methods a load-line is usually introduced which can be achieved by introducing a resistor to increase the output resistance of the power converter or by imposing a scheme whereby the voltage setpoint of the converter changes in proportion to the output current
Systems implemented according to passive current share principles often utilize the droop method. Such methods may introduce resistors in order to increase the output resistance of the power converters to improve matching. For example two power converters with a common output voltage would share current, assuming all other things being equal, according to the ratio of their output resistances, so converters with output resistances of 0.1 milli-Ohms and 0.2 milli-Ohms would mismatch by a factor of 2, i.e. 0.2/0.1. But introducing a 1 milli-Ohm resistance into each converter would significantly reduce the mismatch to 1.2/1.1. The additional resistance introduced must be large compared to the output resistance because the value of the output resistance is unknown and therefore it is important that the resistance introduced dominates the original value. Also, the additional resistors increase the power losses in the system and reduce the efficiency. An effective resistance may be implemented in such systems without introducing a physical resistor by introducing a load-line into the controller. In such systems the voltage-setpoint is reduced in proportion to the current being delivered, giving the power converter a larger output resistance (or load-line) without incurring the power losses of a physical resistor.
Passive current share systems, i.e. load-line or droop, do not require a current share bus and therefore can be used when a current share bus is not available or when a slow digital bus is utilized. However, the droop introduced in the output voltage may be unacceptable in many situations because the value of the interconnect resistance is unknown and therefore a large load-line value is required.
Active current share methods are preferred because of losses and/or excessive output voltage deviation incurred in passive methods. Active methods require a current controller in each converter and a current share bus to convey information to all of the parallel converters regarding the required setpoint for the current being controlled by each converter's current loop. An analogue current share bus can react quickly to changes in converter current error, however it can be sensitive to noise. A digital current share bus can be insensitive to noise, but is limited in the transfer rate of data between controllers which limits the reaction time of the current loop leading to excessive mismatch during transients.
Systems implemented according to active current share principles utilize a common current share bus. Usually this is analogue as described in chapter 12 of “Dynamic Analysis of Switching-Mode DC/DC Converters” by Kislovski, Redl and Sokal (1991). Digital systems also exist, for example see “System Modeling and Digital Control in Modular Masterless Multi-phase DC-DC Converters” by Yang, Zane and Maksimovic, Power Electronics Specialists Conference, 2006. However the digital bus speed can lead to significant delays in balancing the currents (see for example FIG. 10 of Yang et. al 2006).
Therefore what is required is a current share system comprising a speed limited digital communication bus operable during current transients.
This solution is achieved with a system according to the independent system claim and a method according to the independent method claim. Dependent claims relate to further aspects of the present invention.
The present invention relates to a system comprising a plurality of power converters connected in parallel. Each power converter of the plurality of converters comprising an adaptive controller is configured to adaptively alter an output resistance of the power converter by adaptively altering a load line of the power converter comprising an effective resistance and offset voltage such that a difference between each current being supplied by each power converter of the plurality of power converters into a common load is minimized.
The load line of the power converter may be altered such that a difference between each output resistance of each power converter of the plurality of the plurality of power converters is minimized.
For this purpose, each power converter of the plurality of power converters may comprise means for identifying the output resistance of each power converter of the plurality of power converters. Such means may not necessarily identify the parameters explicitly, but may adapt the parameters in order to optimize towards an equal current condition.
Moreover, a negative loadline may be introduced by the adaptive controller, whereby the voltage setpoint increases with current, thereby allowing a negative output resistance for the converter which when utilized in a power system with an interconnect resistance, has the capacity to cancel the interconnect resistance completely such that zero droop is introduced into the final output voltage of the interconnected system.
One aspect of the present invention relates to a digital communication bus that is connecting each adaptive controller of each power converter of the plurality of power converters to each other. The communication bus may be configured to communicate the output resistance of each power converter, the current supplied by each power converter or a current share.
Thus, the system is operable in conjunction with the communication bus conveying information involved in the adaptive system such as average current, estimated resistance or offset voltage or the like. The adaptive controller updates the estimated output resistance at a low rate, e.g. 10 kHz to 100 kHz.
The bus can be configured to communicate additional useful information between converters as well that may indicate status or configuration information between the devices. The system shall be robust versus bus faults because of its adaptive nature.
Operating adaptively, online, and connected by a digital bus, the system of controllers may adjust their load-lines continuously taking information passed between controllers into account to manage the current share and other aspects of power management such as fault, on/off, synchronisation and phase interleaving.
Thus, the power system comprises a current share system allowing parallel power converters to share current on a common output voltage utilizing a digital bus whereby the current control system is operable to control the current during current transients even though the digital bus speed is limited.
Moreover, by use of a digital communication bus, the power converters can communicate fault and status information between one another leading to advantages in reconfiguration and fault management.
The present invention further relates to a method for controlling a system comprising a plurality of power converters connected in parallel. The method comprises identifying an output resistance or an output current of each power converter of the plurality of power converters; communicating the output resistance or the output current of each power converter to each other power converter of the plurality of power converters; and adaptively altering the load line of each power converter such that that a difference between each output current being supplied by each power converter of the plurality of power converters into a common load is minimized and/or such that a difference between each output resistance of each power converter of the plurality of the plurality of power converters is minimized. The method may further comprise communicating a current share to each power converter of the plurality of power converters.
These and other advantages, aspects and novel features of the present disclosure, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.
Reference will be made to the accompanying drawings, wherein:
A power stage is shown in detail in
Returning to
Considering the output resistances R1, R2, R5, R6 that represent resistances inside the voltage loops and therefore contribute to the closed loop output resistances and the interconnect resistances R3, R4, R7, R8 to a star point load represented by ‘I’ involved in the connection between parallel converter outputs, it can be understood that the most accurate balancing or sharing of currents according to the droop method and minimizing the voltage droop, must involve a knowledge of the entire output resistance including interconnect. In order to achieve this means 114, 214, 314, 414 (28 in
Each controller 111, 211, 311, 411 adaptively alters the output resistance and offset voltage of the respective DC-DC converter by altering the load-line of the converter.
The adaptive controller 111, 211, 311, 411 is operable in each converter, adjusting the loadline in order to minimise the difference between the output resistances of the converters and/or equivalently minimise the difference between the currents being supplied by the converters into a common load.
For this purpose, the communication bus 18 is configured to communicate the output resistance of each power converter or the current supplied by each power converter or the current share to each other power converter.
The adaptive controller may operate on principles such as LMS, RLS filters and the like. Also Bayesian update mechanisms may be employed yielding the advantage that information regarding the uncertainty is included in the identification.
Furthermore, the load-line controller is able to introduce a negative loadline whereby the voltage setpoint increases with current, thereby allowing a negative output resistance for the converter which when utilised in a power system with an interconnect resistance, has the capacity to cancel the interconnect resistance completely such that zero droop is introduced into the final output voltage of the interconnected system.
Consider that a load-line in each controller is introduced corresponding to 0.5milli-Ohms and therefore the total mismatch between converters total output resistance corresponds to the difference in R3, 4, 7, 8. If point of load module POL 2 is elected as a “master” then all of the other POL controller's loadlines are desired to adapt until the total resistances are equal and the currents match.
The detail of
The model of the adaptive controller is shown in
Novel features include an adaptive controller for current share in each power converter. The adaptive controllers can be connected by relatively slow bus. Moreover, there is no need to have closed loop control scheme.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/060995 | 5/27/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61828319 | May 2013 | US |
