DE102014225827A1 - Method for operating a DC-DC converter - Google Patents

Abstract

A method and an arrangement (10) for operating a DC-DC converter are presented. An algorithm is used that represents a linear MISO block.

Description

The invention relates to a method for operating a DC-DC converter and an arrangement for carrying out the method.

State of the art

DC-DC converters, also referred to as DC / DC converters, are electrical circuits that convert a DC input voltage to a higher, lower, or inverted voltage level DC voltage. The conversion usually takes place with the aid of a periodically operating switch and an energy store or a plurality of energy stores.

In motor vehicles, DC-DC converters are used in particular in multi-voltage networks, as they are used, for example, in hybrid vehicles. Intensive efforts are currently being made in the automotive industry to develop hybrid propulsion systems in automobiles. Typically in automotive multivoltage networks there are 12 V networks for conventional consumers and 48 V networks for the newer generation consumers. Hence the need to switch between the two networks. For this purpose, inverse converters (English buck-boost converter) have proven to be suitable.

Disclosure of the invention

Against this background, a method with the features of claim 1 and an arrangement according to claim 7 are presented. Embodiments result from the dependent claims and the description.

The method and arrangement presented herein provide a software solution that meets all requirements, exhibits sufficient dynamic performance without the use of hardware, and only requires limited computational capacity.

The presented algorithm implementing the method was originally developed as a fast reactive software component to control a DC to DC converter unit in a motor vehicle. It is necessary to ensure safe operation of both the batteries and the consumers involved, which are connected to the DC-DC converter. This leads to stringent requirements and limitations in addition to the regulation of the output voltage and the output current.

The method in turn is particularly suitable for all electrical or technical systems in which the signal propagation time is at least a factor of 10 smaller than the sampling time and in which the change in the input and output variables have a direct physical connection to one another.

The developed algorithm is particularly suitable for controlling the output voltage and / or the output current to a given target value, limiting the output current, controlling the minimum level of the input voltage and the maximum level of the input current using a single linear regulator, both operates in both voltage and current control modes without the need for cascaded or switched mode controllers.

• 1. Regeln der Ausgangsspannung, um einen Zielwert einzuhalten, mit Strombegrenzung,
• 2. Regeln des Ausgangsstroms, um einen Zielwert einzuhalten, innerhalb des minimalen und maximalen Niveaus der Ausgangsspannung,
• 3. Begrenzen des Ausgangsstroms auf einen variablen Pegel, dieser ist in der Lage, zum Stromregulierungsmodus zu schalten, um einen Vielwert innerhalb des minimalen und maximalen Niveaus der Ausgangsspannung zu halten,
• 4. Begrenzen des Eingangsstroms auf einen variablen Pegel durch Verringern der Ausgangsspannung,
• 5. Schützen der elektrischen Speichereinrichtung durch Verhindern, dass die Eingangsspannung unter einen variablen minimalen Pegel fällt, wobei die Ausgangsleistung verringert wird,
• 6. Begrenzen der Leistung auf der Eingangs- oder Ausgangsseite bei einem variablen Niveau durch Verringern der Ausgangsspannung.

The algorithm performs the following tasks simultaneously:

• 1. regulating the output voltage to meet a target value, with current limiting,
• 2. regulating the output current to meet a target value, within the minimum and maximum levels of the output voltage,
• 3. limiting the output current to a variable level, capable of switching to the current regulation mode to maintain a multivalue within the minimum and maximum levels of the output voltage,
• 4. limiting the input current to a variable level by reducing the output voltage,
• 5. Protecting the electrical storage device by preventing the input voltage from falling below a variable minimum level, thereby reducing output power.
• 6. Limiting the power on the input or output side at a variable level by reducing the output voltage.

The presented method is characterized in that only one controller is used by the algorithm representing a voltage mode controller. The target value of the controller is modified with the processed and cascaded values of the error signals. The final result of the solution is a complex but very simple code. This is a discrete linear MISO (Multiple Input Single Output) block. All limits can be dynamically modified by the application.

This architecture may be useful if the control signal is the same in each working mode. The biggest advantage is that the controller complies with the linear transfer characteristic between the working limits as the system goes to different states, taking into account the working environment. Therefore, the transitions of the system are linear and continuous, which improves the stability and robustness of the control. Furthermore, the lack of cascade connections ensures better dynamic behavior for the overall system. The key element is the conversion and binding of the input error signals. The method can be used with most types of controllers.

The method described is used, for example, in conjunction with a DC-DC converter, in which the switching elements are controlled by a time-controlled PWM generator. No hardware current controller is used. For the converter, the transfer function _of U / U must be _a valid. The propagation time of the signals taking into account each other are orders of magnitude faster than the sampling time. Due to the relatively long sampling time, the system can not be divided into differently timed processes.

It should be noted that the automotive application environment places high demands on the voltage regulator algorithms of the converter. The main requirements of the controller correspond to the requirements of the inverter in both directions. A time varying, nonlinear higher order power conversion system is presented which operates stably at all operating points.

The time variance is due to the dependence of the transfer function on the load resistance, the nonlinearity in the resistors, the inductances, the capacitances and the power transistors as well as the high variance in the input and output voltages.

Furthermore, a high dynamic for a coupled power electronics is provided in all operating points. Voltage and current limits are maintained at the input and output. The performance is held.

Furthermore, the code is adapted to limited capacities, runtime limitations and limited sampling rates. Thus, the controllers have to work at lower sampling rates.

The operation of the algorithm is basically based on the close and simple physical connection of the various inputs and outputs. This means that the input signals can be transformed among each other with actual simple mathematical functions.

Thus, an adaptive, discrete MISO multifunction algorithm with a single regulator for DC-DC converters is presented. The algorithm developed is characterized by the fact that it uses only a simple linear controller.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

1 shows an embodiment of the arrangement.

2 shows an input current limiting unit.

3 shows in a graph the frequency response as a function of the load

4 shows in a block diagram a multi-input controller

Embodiments of the invention

The invention is schematically illustrated by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

1 shows the structure of the arrangement or controller arrangement, the whole with the reference numeral 10 is designated and used to carry out the presented method. The illustration also shows a DC-DC converter 12 that of the arrangement 10 is controlled.

In addition, the illustration shows a gain adjustment 14 , a regulator 16 , in particular voltage regulator, in this case a PID controller, an output current limit 18 , an input current limit 20 , an input voltage limit 22 , Furthermore, a unit 24 for load detection, a first block 28 selecting a minimum value, a second block 30 which selects a minimum value and a member 32 , which performs the function ≥ 0, provided. It goes in as a controlled variable, a voltage U _set 40 , a supply voltage U _supply 42 , a maximum output current I _{off, max} 44 , a maximum supply _current I _{supply, max} 46 and a minimum supply voltage U _{supply, min} 48 ,

Output variables of the DC-DC converter 12 are a voltage U 50 and a current I 52 , Input of the DC-DC converter 12 and thus manipulated variable is the duty cycle 54 ,

As part of the voltage regulation by means of the voltage regulator 16 In the above converters, the duty ratio determines the ratio between the input and output voltages. The control signal as control variable of the control is the duty cycle, which physically determines the ratio between the input and output voltage. Therefore, the control is independent of the reference signal. The control function is generally a PID block. The type of regulator can vary, however.

At the output current limit 18 the applied current control is an indirect process based on Ohm's law and voltage regulation. The algorithm estimates the current resistive load of the DC-DC converter 10 and generates a voltage value with it and with the actual maximum current. If this value is less than the current target voltage, the target size will be replaced by the lower value. R _estimated = U / I (1) U _out = I _{out of} R _estimated (2)

2 illustrates in a block diagram the input current limit, which in 1 with reference number 20 is designated. The illustration shows an input 70 for a parameter regarding a maximum input current and an input 72 for a parameter relating to a maximum output current. There is also an entrance 74 provided for the duty cycle, size at the output 76 is a maximum output current. Furthermore, there is an efficiency block 80 and a block 82 which selects a minimum value.

The following applies:

By exploiting the switching DC-DC converter, the limiting method can be extended. The voltage ratio and the efficiency of the converter, resulting in block 80 is representiert, determines the relationship between the input and output voltage. Therefore, the actual input current value can be easily converted to the output side. After comparing the two values, the lower than the actual current limit is considered.

For input / output power limitation, the current limiter structure is extended with mathematical formulas to consider power limits. In some cases it is necessary if the input or output voltage is in the highest working range. In these cases, the output power could exceed the nominal value of the unit and cause an overload situation without violating the current limits.

The simple Min () function ensures that the lowest of all calculated values will always be valid.

In the current control mode, using a simple logic switch in the module at the current limiter output, the structure can be switched to a full function current regulator mode, and the input is given the target current value.

When monitoring the input voltage level, what in 1 through block 22 is realized that in many cases the power source of the motor vehicle does not provide enough power to maintain the voltage level of the energy storage unit. Therefore, the converter unit must consider the minimum of the voltage on the input side, and must secure a minimum input voltage level by controlling the output power, taking into account the vehicle power management command. This is the most complex situation for the controller. However, the conversion of the values for this case is also given. To increase the robustness of the system, an additional auxiliary controller is integrated into the control loop. This reduces the actual target voltage of the main regulator when the input voltage reaches the minimum level and forms a reverse control loop.

In the parallel work modifier, simply summing the modifying signals of the inputs results in parallel processing, a stronger constraint can be active at the same time, but the system provides the highest possible performance, without the need for expensive determining software.

The various delimiters establish a natural order of priority for the physical behavior of the system.

• 0. maximaler Versorgungsstrom
• 1. maximaler Ausgangsstrom
• 2. Halten der Ausgangsspannung oder des Ausgangsstroms bei dem Zielwert

The natural order is:

• 0. maximum supply current
• 1. maximum output current
• 2. Holding the output voltage or the output current at the target value

A lower atomic number means a higher priority. If necessary, the order may be affected by using a simple decision logic to obtain a more flexible application, such as through the switch in the current control or current limiter mode.

In the gain adjustment, the in 1 through block 14 is realized, the regulated system is heavily dependent on the load. The disadvantage of the linear regulators is that they can perform maximum dynamic performance in a relatively narrow range around a single operating point without risking instability. In response to the challenge of the time variant system, the gain scheduling method, which considers the dynamic change in control settling versus actual situation, was used to account for and compensate for the effect of the wide range of dynamically changing load.

Based on the measured data, the gain planning table was created. This method increases the robustness of the closed loop for a wide variety of external loads. With this extension, the converter can supply both an open connection and a load of 10 mOhm, similar to a short circuit. 3 explains how the transfer function changes depending on the load. Note that in practical applications, the main controller is a single integrator part, which makes gain planning very easy.

3 shows in a graph the frequency response as a function of the load. The size [dB] is entered at the top and the phase [deg] at the bottom. In this case, the characteristic of the open circuit of the arrangement in the case of different ohmic loads at a duty cycle of 30% is entered from an input of the duty cycle to the output to the DC-DC converter starting at 0.025 O to 100 O in seven steps.

When the system reaches a limit, the controller begins to reduce the output power linearly to monitor the value at the limit until it is physically possible. If the operating conditions are outside the controllable range, then the device must go into the fail-safe state. If the conditions are normalized then the facility will continue to work error free.

The presented process has a number of advantages. Thus, the software control ensures the time invariance of the controller during the entire lifetime. Due to the continuous voltage control, there are no transitions between operating ranges or operating points. The adaptive control loop achieves maximum dynamics and stability. Despite non-linear hardware elements, the process is stable and robust. The code size is also extremely compact.

The algorithm is easy to set, maintain and adapt to other facilities. This leads to a reduction in development time. The architecture presented may also be useful for other systems where the control signal is the same in all working modes. In addition, a transparent and flexible code is achieved.

4 shows in a block diagram the theoretical signal flow diagram of a controller with multiple input. There are provided a first entrance 100 for a maximum supply current, a second input 102 for a supply current, a third input 104 for a minimum supply voltage, a fourth input 106 for a supply voltage, a fifth input 108 for the controlled variable U _set , a sixth input 110 for a maximum output current, a seventh input 112 for an output current, an eighth input 114 for a selection signal, whether a soak or current control is performed, a ninth input 116 for a discharge voltage and a tenth input 118 for an estimated load.

Furthermore, an input current limit 130 that in block 18 of the 1 integrated, an input voltage limit 132 according to block 22 out 1 and an output current limit 134 matched block 18 of the 1 shown.

The illustration also shows saturation blocks 140 . 142 and 144 to make sure that the outputs stay negative, and a selector switch 146 Regarding current limitation / regulation. Furthermore, a gain adjustment 150 according to block 14 in 1 and a voltage control 154 according to block 16 in 1 shown.

Simply adding the errors results in parallel work. Another limit is active at the same time, resulting in a natural priority stemming from the physical behavior of the system for which the method was developed.

• 0. minimale Versorgungsspannung,
• 1. maximaler Versorgungsstrom,
• 2. maximaler Ausgangsstrom,
• 3. Halten der Ausgangsspannung oder Ausgangsstroms bei Zielwert.

The natural order:

• 0. minimum supply voltage,
• 1. maximum supply current,
• 2. maximum output current,
• 3. Hold the output voltage or output current at target value.

A lower atomic number means a higher priority.

If necessary, the order in which a simple arbitration logic is used to obtain a wider implication field, such as the switch between current control and current limiter mode, may be affected.

Claims (9)

Method for operating a DC-DC converter ( 12 ), the output voltage of which is regulated, whereby in the context of an algorithm a regulator ( 16 ), which represents a voltage mode controller and outputs a duty cycle as a manipulated variable, is used, the algorithm representing a linear MISO block. Method according to Claim 1, in which a gain adaptation ( 14 ) is made. Method according to Claim 1 or 2, in which an output current limitation ( 18 ) is carried out. Method according to one of claims 1 to 3, in which a power limitation is performed. Method according to one of claims 1 to 4, in which as regulator ( 16 ) a PID controller is used. Method according to one of claims 1 to 5, which in conjunction with a DC-DC converter ( 12 ) is used, are controlled in the switching elements by a timed PWM generator. Arrangement for operating a DC voltage regulator ( 12 ), which is set up in particular for carrying out a method according to one of claims 1 to 6. the arrangement ( 10 ) implements an algorithm that includes a controller ( 16 ), which represents a voltage mode controller and outputs a duty cycle as a manipulated variable, the algorithm representing a linear MISO block. Arrangement according to claim 8, in which as regulator ( 16 ) a PID controller is used. Arrangement according to claim 8 or 9, which is designed for use in a motor vehicle.

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