WO2019161875A1

WO2019161875A1 - Method and circuit for multilevel modulation

Info

Publication number: WO2019161875A1
Application number: PCT/EP2018/025229
Authority: WO
Inventors: Stefan GÖTZ
Original assignee: Dr. Ing. H.C.F. Porsche Aktiengesellschaft
Priority date: 2018-02-20
Filing date: 2018-09-06
Publication date: 2019-08-29
Also published as: DE102018103711A1

Abstract

Method for multilevel modulation, in which method a multilevel converter, which comprises a plurality of controllable switches, is actuated by an output signal (204) of an electronic circuit (200), wherein a reference signal which is applied to an input (202) of the electronic circuit (200) is split into a multilevel base signal and a residual value by way of the reference signal being output from a signal former (210), as a multilevel base signal (206), to prespecified quantization levels in the electronic circuit (200), said multilevel base signal (206) being subtracted from the reference signal by a subtractor and therefore the residual value being formed, the residual value being digitized by a two-level modulator (212) and being combined with the multilevel base signal (206) by an adder, as a result of which the output signal (204) of the electronic circuit (200) is formed.

Description

Method and circuit for multilevel modulation

The present invention relates to a method and a circuit to a

Multilevel modulation, in which a modulation of an input signal by splitting into two parts is effected.

Power electronic circuits use semiconductors almost exclusively as switches and avoid lossy resistive operation. By means of a

Switching modulation, for example, executed in the most common variant as pulse width modulation with fixed clock, a continuous output voltage and in particular intermediate values between discrete switching stages are generated from a few available discrete switching stages. In terms of time, the output value (voltage or current) corresponds to a specification. conventional

DC-DC converters and inverters usually use only a very small number of stages or levels, often only two. Intermediate values between two levels are then approximated by temporal alternation between a respective upper and lower level. Central disadvantage is a generation of

Switching harmonics in the electromagnetic spectrum. The representation of the output voltage by switching modulation with discrete current or voltage values is called a modulation and the associated method as a

Modulator designated. Various methods, in particular those which form an error signal in the past or the future, for example a sigma-delta modulation, model predictive modulation or PI control method further comprise a quantizer, which decides which of the two levels to set based on an error signal , For a two-level system, quantization is easy to implement because, for example, only a tendency or a sign of the error signal must be used in order to reduce the error signal at the next set level. For example, DE 10 2007 020 477 A1 describes a sigma-delta modulator with a control loop in which a multi-level quantizer and a multilevel digital-to-analog converter are arranged. The multilevel digital-to-analog converter is realized with a plurality of unitary electrical elements, wherein dynamic and static deviations between the unitary electrical elements are determined among each other.

Modular multilevel converters can be unlike a traditional multilevel converter

Power electronics, with a few power semiconductor switches on and / or

Switching output voltages between a few levels in order to effect a desired voltage on average, a voltage through a dynamically changeable electrical configuration of energy stores arranged in modules, eg.

Provide capacitors or batteries in very fine steps. A central

Multilevel converter in this sense is the modular multilevel converter MMSPC described by S. M. Goetz, A.V. Peterchev and T. Weyh, "Modular Multilevel

Converter With Series and Parallel Modules Connectivity: Topology and Control, "in IEEE Transactions on Power Electronics, vol. 30, no. 1, pp. 203-215, Jan. 2015. Other well-known multilevel topologies include a neutral point clamp Inverter or a flying capacitor inverter realized.

In particular, when modulators using quantizers are transferred to a multi-level system, there is a problem that in the prior art

Multilevel quantizer must be used. The multilevel quantizer, unlike the above-mentioned two-level quantizer, involves not only the sign of the error signal or an equivalent signal but also its magnitude. For example. For example, for a five-level inverter (level -2, -1, 0, 1, 2), the level 0 error signal can be reduced only very slightly with a negative sign, +1 faster and +2 fastest. In particular with inductive loads and voltage-controlled inverters, this can be used to control a current gradient, resulting in a open degree of freedom results. However, this open degree of freedom also causes problems.

Thus, typical multilevel quantizers are tuned to a specific useful frequency range. In the case of a high bandwidth of useful signals, for example in drives, either the gain of the multilevel quantizer must be continuously adapted or it must be expected that, for example, at low frequencies more output stages will generally be switched at once than comparatively at high frequencies. In particular, this problem occurs as soon as the error signal is subjected to a filter. While the error signal may be in the same unit as the quantized output stage (e.g., in volts) and correspondingly easy to derive generally valid quantization levels (eg the maximum output voltage swing divided by the number of levels), this is very difficult for the filtered signal possible. The filtered signal represents a combination of the absolute signal, its derivative and its integral, and a determination of quantization levels can only be achieved with information from a derivative, a frequency or an integral of the signal. If necessary, a natural quantization can not be derived at all. This situation is particularly disadvantageous in sigma-delta modulators. A conventional sigma-delta modulator typically forms the error signal as

Difference between the continuous target signal and the quantized output signal (here two levels, i.e. +1 or -1). This error signal is formed in a continued embodiment and guided into a filter, which is realized, for example, in the simplest case by an integrator. The output of the filter is passed to the quantizer, which

correspondingly forms a 1 / + 1 sequence as a quantized output signal, which as

Digital signal is sent to the power electronics and causes the opening / closing of the respective switch in this.

The sigma-delta loop may be continuous or timed so that a new value is formed for each clock. This loop can act like a PID controller (from Expert abbreviated to proportional-integral-derivative-controller) are considered to a quantizer: The PID controller minimizes the control error of the quantizer. As a feedback output, the quantized output signal or even a physical measurement value, for example, the output voltage or the

Output current to be used.

In a multilevel system, the quantizer would have to, as above

described, can discriminate several levels and thus decide from which error size he sets what value at the output. This requires a sensitivity adjustment. However, this sensitivity setting should depend on the filter in a sigma-delta modulator and take into account the spectral component of the signal. However, if the signal contains more than one frequency, the sensitivity setting is no longer easily possible. The publication DE 10 2011 082 946 B4 now discloses the decomposition of a multi-level quantized reference signal into partial signals. The respective sub-signals are then provided by means of different energy cells, so that the average load of the respective energy cells is the same. Against this background, it is an object of the present invention to provide a method which solves the problem of multilevel quantization with already existing and easily provided electronic components and assemblies. Furthermore, it is an object of the present invention to provide a corresponding system for carrying out such a method.

To solve the above object, a method becomes a

Multilevel modulation proposed in which a multilevel converter, which comprises a plurality of controllable switches, is driven by an output signal of an electronic circuit, wherein a signal applied to an input of the electronic circuit reference signal is split into a Multilevelsockelsignal and a residual value is in the electronic circuit, the reference signal is output from a signal generator as Multilevelsockelsignal on predetermined Quantisierungsleveln, this Multilevelsockelssignal is subtracted from the reference signal by a subtractor and thus the residual value is formed, the residual value by a

Zweilevelmodulator is digitized and by an adder with the

Multilevelsockelsignal is merged, whereby the output signal of the electronic circuit is formed.

The solution splits the signal into a multilevel socket signal and a residual value, where the multilevel socket signal is used unfiltered, such that natural

Quantization level can be specified while the residual value a

ordinary two-level modulator is passed.

The predetermined quantization levels result from a number of levels in a multilevel converter, which is used by a system implementing the method according to the invention. Through the solution, almost every previously known two-level modulator can be converted into a multilevel modulator.

In one embodiment of the method according to the invention, either a voltage or a current is selected for the output signal, reference signal and multilevel base signal. The inventive method can be depending on the design of a

Control, for example, an electric drive machine for voltages or currents alike perform. In a further embodiment of the method according to the invention, in the signal generator of the predetermined quantization levels that quantization level is selected which represents a nearest neighbor to the reference signal. This takes into account that it is advantageous, for example, in a power electronics, and in particular in a multi-level power electronics comprising a multilevel converter, when only a minimum number of Semiconductor switches their state changes. In this way, switching losses are minimized, which usually increase with the number of power semiconductors to be switched.

In a further further embodiment of the method according to the invention, the nearest neighbor is rounded off or rounding or rounding to zero or rounding to plus or minus infinity, or a commercial rounding of a difference between the quantization level associated with that

Reference signal represents a smallest difference, and formed the reference signal.

Other forms of the next neighbor education, for example, from temporal integration, are conceivable.

In a still further embodiment of the method according to the invention, a power semiconductor switch is selected as the respective controllable switch. These are used in particular in the multilevel power electronics.

In a further embodiment of the method according to the invention, a filtered error signal is generated at an output of the two-level modulator, which is fed back with an input signal of the two-level modulator. The method according to the invention may advantageously be implemented with a large number of modulators which generate a filtered error signal and form its output on the basis of this. In particular, a sigma-delta modulator can be selected as a two-level modulator.

Furthermore, a circuit for a multilevel modulation having an input and an output is claimed, which comprises a signal generator, a two-level modulator, a subtractor and an adder, wherein the signal generator is adapted to output a voltage applied to the input of the circuit reference signal as Multilevelsockelsignal on predetermined quantization levels in that the subtractor is adapted to subtract that multilevel pedestal signal from the reference signal and thereby form a residual value, the bi-level modulator is adapted to digitize this residual value, and the adder is adapted to do so with the multilevel pedestal signal an output signal at the output of the circuit merge, whereby a present at the input of the circuit reference signal is split into a present at the output of the circuit Multilevelsockelsignal and the residual value. In an embodiment of the circuit according to the invention, the two-level modulator is a sigma-delta modulator. The circuit according to the invention can generally use, as a two-level modulator, modulators which generate a filtered error signal and form its output on the basis of this. Finally, a system for a multilevel modulation is claimed, which includes a circuit according to the invention, a multilevel converter, at least one

Energy storage unit, a reference signal generator, and a power or

Voltage source which feeds the Referenzsignalbildner, and which is adapted to carry out the inventive method.

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 respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention.

The figures are described coherently and comprehensively

Components are assigned the same reference numerals.

FIG. 1 shows a schematic representation of a splitting of a reference signal into a multilevel base signal and a residual value by execution of an embodiment of the method according to the invention. Figure 2 shows a schematic representation of an embodiment of a circuit according to the invention, with the execution of an embodiment of the method according to the invention, a splitting of a reference signal into a

Multilevelsockelsignal and a residual value is effected.

Figure 3 shows a schematic representation of an embodiment of a

circuit according to the invention, which is equipped with a sigma-delta modulator.

In Figure 1 is a schematic representation of a 100 by execution of a

Embodiment of the inventive method caused splitting of a

Reference signal 112 shown in a multi-level base signal 122 and a residual value 132. The sinusoidal reference signal 112 is shown in graph 110, with a time axis 102, here by way of example with the unit millisecond, and an amplitude axis 104 with the unit volt. The multilevel socket signal 122 is in graph 120 with the same

Axis units shown. It will be at one time at a time

Receive quantization level, which represents a nearest neighbor to the reference signal 112. As long as the multilevel base signal 122 dwells at the respective quantization level, this does not result in a change of a power semiconductor switch position in a corresponding multilevel converter. The from the reference signal 112 through

Subtraction of the multilevel base signal 122 resulting residual value 132 is shown in graph 130. Again, the physical units of the axes 102 and 134 are equal to the graphs 110 and 120, however, with the amplitude axis 134, the scale is increased. In Figure 2 is a schematic representation of an embodiment of the

Circuit 200 according to the invention, by means of which one embodiment of the method according to the invention splits a reference signal applied to input 202 shown in graph 110 into a multilevel base signal 206 shown in graph 120 and a residual value shown in graph 130 , A signal generator 210 outputs the reference signal applied to the input 202 as Multilevelsockelsignal 206 on predetermined quantization levels. This is subtracted in a subtractor indicated by the symbols "+" and from the reference signal applied to the input 202. The residual value thus formed, represented in graph 130, is then supplied to a two-level modulator 212

Two-level modulator 212 digitized residual value is combined in the designated by the symbols "+" and "+" adder with the multi-level base signal 206 to an output 204. For example, a multilevel converter or the power semiconductor switch encompassed by the latter is triggered by the output signal 204. In Figure 3 is a schematic representation of an embodiment 300 of

inventive circuit shown in Figure 2, which is equipped with a sigma-delta modulator. The multilevel base signal formed by signal generator 310 is applied to a first subtractor labeled "+" and in which it is subtracted from the reference signal applied to input 202, and as residual value 308, subtracted by "+" and "2"

designated subtractors, a filter 312 and a binary quantizer 314 formed sigma-delta modulator, the

Zweilevelmodulator 212 of Figure 2 represents supplied. The signal output by the sigma-delta modulator is on the one hand via the second subtractor with the

Residual value 308 fed back, on the other hand to the adder designated by the symbols "+" and "+" combined with the Multilevelsockelsignal 206 to an output signal 204.

Claims

claims

1. A method for a multilevel modulation, in which a multilevel converter, which comprises a plurality of controllable switches, is driven by an output signal (204) of an electronic circuit (200, 300), wherein an input (202) of the electronic circuit (200, 300) applied reference signal (112) in a

Multilevelsockelsignal (122) and a residual value (132, 308) is split by in the electronic circuit (200, 300), the reference signal (112) of a

Signal generator (210, 310) as a Multilevelsockelsignal (122, 206) to predetermined

Quantization level is output, this multilevel base signal (122, 206) is subtracted from the reference signal (112) by a subtractor and thus the residual value (132, 308) is formed, the residual value (132, 308) is digitized by a two-level modulator (212) and is summed by an adder with the multi-level base signal (112, 206), whereby the output signal (204) of the electronic circuit (200, 300) is formed.

The method of claim 1, wherein one of a voltage and a current is selected for the output signal (204), the reference signal (112), and the multilevel base signal (122, 206).

3. The method according to any one of the preceding claims, wherein in the signal generator (210, 310) of the predetermined quantization levels that quantization level is selected, which represents a nearest neighbor to the reference signal (112).

4. The method of claim 3, wherein the nearest neighbor is rounded up or rounded or rounded to zero or rounded to plus infinity or minus infinity, or a commercial rounding of a difference between the quantization level associated with the reference signal (112). represents a slightest difference, and the reference signal (112) is formed.

5. The method according to any one of the preceding claims, wherein as the respective controllable switch, a power semiconductor switch is selected.

6. The method according to any one of the preceding claims, wherein at an output of Zweilevelmodulators (212) a filtered error signal is generated, which is fed back with an input signal of Zweilevelmodulators (212).

7. The method of claim 6, wherein as a two-level modulator (212) a sigma-delta modulator is selected.

8. A multilevel modulation circuit (200, 300) having an input (202) and an output (204), which comprises a signal generator (210, 310), a two-level modulator (212), a subtractor and an adder, wherein the signal generator ( 210, 310) is adapted to be applied to the input of the circuit (200, 300)

Reference signal (112) as a Multilevelsockelsignal (122, 206) to predetermined

Output quantization levels, the subtractor is designed to this

To subtract multilevel base signal (122, 206) from the reference signal (112) and thereby form a residual value (132, 308), the two-level modulator (212) is adapted to digitize this residual value (132, 308) and the adder is designed to merge this with the multilevel base signal (122, 206) into an output signal (204) at the output of the circuit (200, 300), whereby the reference signal (112) present at the input (202) of the circuit (200, 300) is applied to the output signal (204) the multilevel base signal (132, 306) present in the circuit (200, 300) and the residual value (132, 308) are split.

The circuit of claim 8, wherein the two-level modulator (212) is a sigma-delta modulator.

10. A system for multilevel modulation comprising a circuit (200, 300) according to claim 8 or 9, a multilevel converter, at least one energy storage unit, a reference signal generator, and a current or voltage source feeding the reference signal generator, the system being adapted to carry out a method according to one of claims 1 to 7.