AT523577A1 - Machine converter and method for operating a machine converter - Google Patents

Abstract

The invention relates to a machine converter for supplying an N-phase electrical machine (1) with alternating current from a DC voltage source, for example a battery, a fuel cell or a DC voltage intermediate circuit, whereby for at least one, preferably each of the N phases of the electrical machine (1) M electronically controllable half bridges (2, 2 ', 2a, 2a', 2b, 2b ') are provided, where M is greater than one, a control unit driving the half bridges (2, 2', 2a, 2a ', 2b, 2b') in pulse width modulation (3) is provided, and the control unit (3) is designed to activate the half bridges (2, 2 ', 2a, 2a', 2b, 2b ') at least one, preferably each of the N phases in such a way that the Current of this phase is divided essentially equally between the M half-bridges (2, 2 ', 2a, 2a', 2b, 2b ') assigned to the phase. The invention also relates to a loading unit for a test stand with such a machine converter, a method for operating such a machine converter and the use of such a machine converter for operating a loading unit of a test stand.

Description

Machine converter and method for operating a machine converter

The invention relates to a machine converter and a method for operating a

Machine converter.

Inverters for operating electrical machines (machine converters) are known from the prior art. To generate variable alternating voltages, these are designed as switched inverters with semiconductor bridge circuits that use a modulation process, e.g. pulse width modulation (PWM), to simulate a sinusoidal alternating voltage from short high-frequency pulses (a few kHz to over 20 kHz). Such inverters are also referred to as sine wave inverters. The semiconductor switches switch the DC voltage on and off at a high frequency; the mean value of the high-frequency, pulse-width-modulated switching frequency is the output alternating voltage. The output alternating voltage is thus composed of small pulses of different widths; the resulting current approximates that of a normal network

sinusoidal current curve.

Such switched inverters are used in particular in test stands for vehicles, since with such test stands AC voltages of variable amplitude and frequency with high power and at the same time the lowest possible ripple current are required. In test stands from the prior art, the electrical power is made available via a DC voltage intermediate circuit, and machine converters convert the DC voltage into the AC voltage required for the respective electrical machine, for example an electric motor as the load machine of a mechanical drive train.

In such machine converters, at least one half bridge per phase of the electrical machine is controlled by a PWM method via a control device.

One problem with conventional test stands, however, is that the machine converters, due to the high power required, usually over 100 kW, and the high DC voltage, usually over 500 V, are too large to be able to be arranged directly on the electric machine to be driven. Long three-phase connection lines are therefore required, which in turn leads to increased electrical interference. In addition, the pulse width modulation of the high DC voltage creates high-frequency interference, which feed back into the DC voltage intermediate circuit and cause ripple currents in the driven electrical machine. The high switched direct voltage also results in a very high alternating current load on the input-side capacitors due to the block-shaped current.

It is thus an object of the invention to solve at least one of these problems. In particular, a machine converter is to be made available which is compact and can be used in particular in a test stand for vehicles or as part of an electric drive unit of a vehicle without unduly disrupting the DC voltage intermediate circuit and without the driven one

to load electrical machine with ripple currents.

These and other tasks are performed by a machine converter and a method for operating a machine converter according to the independent

Patent claims solved.

A machine converter according to the invention is designed to supply an N-phase electrical machine with alternating current from a direct voltage source, for example a battery, a fuel cell or a direct voltage intermediate circuit. For at least one of the N phases of the electrical machine, M electronically controllable half bridges are provided, M being greater than one. M half bridges can also be provided for each phase.

An electronic control unit controlling the half-bridges in pulse width modulation is provided, which is designed to activate the half-bridges of at least one of the N phases with a time offset in such a way that the current in this phase is divided essentially equally between the M half-bridges assigned to the phase. This results in an increase in the switching frequency of the PWM method by a factor of M and a smoother and more interference-free simulation of a sinusoidal signal can be achieved even at high voltages and high frequencies.

In particular, it can be provided that the electronic control unit is designed to activate the half-bridges of each of the N phases with a time offset in such a way that the current in each phase is divided essentially equally between the M half-bridges assigned to the phase.

The outputs of the half bridges can be fed directly into the electrical machine, for example electrical windings in the machine can be fed directly.

According to the invention, however, it can also be provided that the outputs of those M half-bridges which supply the same phase are connected together via current-compensated interleaving chokes. This has the advantage that a smooth transition between the switched half bridges is possible and interference is reduced. Current-compensated means that the windings of the chokes open in opposite directions

run through a common iron core.

The control unit can be designed to activate the M half-bridges assigned to a phase in each case for an identical switch-on duration ton and with a delay in relation to one another by a period of essentially ton / M. In other words, the switch-on times of the assigned half bridges are essentially of the same length, namely equal to ton, but offset from one another by ton / M. For example, when M = 2, the two half bridges assigned to a phase are activated with a delay of approximately ton / 2 in these exemplary embodiments.

Of course, slight deviations can occur without departing from the scope of protection of the invention; for example, actual delay values of 0.4 x ton-0.6 x ton at M = 2 can also be provided according to the invention. In embodiments with three half-bridges per phase, i.e. M = 3, the half-bridges are each activated with a delay of approximately ton / 3 for a duration of ton, whereby a certain tolerance of the delay values can again be provided,

for example about 0.2 x ton - 0.4 X ton.

This superimposition of the control signals from individual half bridges results in an increase in the switching frequency by a factor of M from the perspective of the activated phase, i.e. approximately a doubling of the switching frequency when M = 2.

The control unit can be designed to generate a pulse-width-modulated control signal of the half bridges with a frequency which is a factor of 5 to 100, preferably a factor of 10 to 20, higher than the frequency of the desired output signal (sinusoidal signal) on the phases. For example, with a frequency of the (sine) output signal on the phase of 1 kHz, a frequency of the pulse-width-modulated control signal of approximately 5 kHz to approximately 100 kHz can be provided. When using appropriately designed semiconductor switches, an even higher frequency of the pulse-width-modulated control signal can also be provided. The superposition of the control signals according to the invention makes this frequency

increased even further, so that a particularly low ripple current can be achieved.

According to the invention, the number of phases N can be equal to three. The number M of half bridges per phase can be two, three, four, five, six or more.

Each of the half bridges can comprise two controlled semiconductor switches Q1, Q2, preferably SiC transistors.

The invention also extends to a load unit for a test stand

a machine converter according to the invention and an N-phase electrical machine.

According to the invention, separate machine windings M are provided in at least one of the N phases in the electrical machine and are insulated from one another, the machine windings of this phase each being led to one of the half bridges. Preferably, in each of the N phases M separate machine windings isolated from one another are provided, the machine windings of each phase being led to one of the M half bridges. In this case, there is no need to use interleaving chokes, since the machine windings themselves lead to the desired superimposition of the current or the magnetic flux in the machine.

According to the invention, it can be provided for particularly high electrical powers that a separate inverter unit, each with M half bridges, is provided for each of the N phases of the electrical machine. A separate control unit can be provided for each of the inverter units, but a common control unit can also be provided for all inverter units.

The invention also extends to a method for supplying an N-phase electrical machine with alternating current from a direct voltage source, for example a battery, a fuel cell or a direct voltage intermediate circuit. In the method according to the invention, electronically controllable half bridges and a control unit controlling the half bridges in pulse width modulation are provided for at least one, preferably each of the N phases of the electrical machine M.

According to the invention, the control unit activates the half-bridges of at least one, preferably each phase, with a time offset in such a way that the current in this phase is divided essentially equally between the M half-bridges assigned to the phase. In particular, the control unit can each have the M half bridges assigned to a phase for an identical switch-on duration ton and by a time offset of

Activate ton / M delayed.

The control unit can be designed as an integrated electronic component, but can also comprise several separate control devices.

The invention also extends to the use of a method according to the invention for operating a load unit of a test stand.

Further features according to the invention emerge from the patent claims, the figures and the following description of the figures. The invention is explained below using non-exclusive exemplary embodiments:

1a shows an embodiment of a machine converter according to the invention when controlling an electrical machine using interleaving chokes;

1b-1c show schematic voltage and current profiles when an embodiment of the method according to the invention is carried out;

2 shows an embodiment of a machine converter according to the invention using an electrical machine with separate windings in each of the three phases.

1a shows an embodiment of a machine converter according to the invention for supplying a 3-phase electrical machine 1, namely an electric motor with the 3 windings U, V and W. The machine converter converts an input DC voltage Voc from a DC voltage intermediate circuit into three phase-shifted AC voltages L1, L2 , L3 to operate the electric motor. For this purpose, the machine converter comprises a bridge rectifier with six half bridges 2, 2 ‘, 2a, 2a‘, 2b, 2b ‘, one phase U, V, W of the electrical machine 1 being supplied via two half bridges. The half bridges each include two electronically switchable semiconductor switches Q: 1, Q2, Q1 ‘, Q2‘, Q1a, Q2a, Q1a ‘, Q2a‘, Q1pb, Qz2b, Q16 ‘, Q26‘, which are connected to an electronic control unit 3. In this exemplary embodiment, the control unit 3 is implemented as an integrated electronic component.

In this exemplary embodiment, the semiconductor switches are designed as SiC switches and have a high dielectric strength.

The control unit 3 switches the semiconductor switches in a pulse width modulation process with a basic frequency of about 5 kHz per switch in order to be able to form the most ideal sinusoidal shape for each of the phases U, V and W. In other words, the frequency of the control signals of a switch is approximately 5 kHz in this exemplary embodiment.

The control unit 3 is designed to activate those half-bridge pairs that supply the same phase of the electric motor with a time delay in such a way that the current of this phase is divided essentially equally between the two half-bridges.

For example, the control unit 3 first activates the first half bridge 2 for a certain period of time ton and, after a delay time of ton / 2, the half bridge 2 ‘for an identical period of time ton. This halves the power transmitted per half bridge and doubles the frequency of the PWM process per phase of the electric motor. As a result, the ripple in the output current decreases and disruptive repercussions in the DC voltage intermediate circuit are also reduced.

In this exemplary embodiment, the outputs of two half bridges each, which supply the same phase, are connected together via current-compensated interleaving chokes 4, 4 °, 4a, 4a, 4b, 4b ‘. Two windings running in opposite directions are provided on a common iron core for each phase. This enables the compact design of the chokes and, at the same time, particularly ripple-free operation of the bridge rectifier.

Fig. 1b shows schematically the time profile of the voltage V at phase L + 1 and the schematic profile of the switch-on pulses for the switches Q1, Q2 of the first half bridge 2 and Q1 ‘, Q2‘ of the second half bridge 2 ‘. This schematic diagram shows how the PWM method works for generating a sine output signal that is as precise as possible. The period of the PWM signal is marked with the symbol T, the duty cycle, i.e. the duty cycle, of the PWM signal rises and falls sinusoidally, the period of the sine output signal is denoted by the symbol Tı1 and is about 20 times higher than T.

Fig. 1c shows the schematically indicated in Fig. 19 detail A in a higher degree of detail, the switching pulses of the switches Q2 and Q2 'and the current Iz through the first half bridge 2, the current I2' through the second half bridge 2 'and the entire current Iges = I2 + l2 'of phase L1: are shown idealized. The two half-bridges are each activated for an identical switch-on duration ton, the second half-bridge 2 being activated with a delay compared to the first half-bridge 2 by the time period ton / 2. In relation to the period duration of the assigned phase, the resulting phase offset is usually less than 1 °, around 0.1 °. From the point of view of phase L1, this results in a doubling of the frequency of the PWM process. The superimposition of the partial currents I2 and I2 ‘reduces the alternating current load on capacitive elements, while the switching frequency of the half bridges remains low. In the present exemplary embodiment, the switching frequency of each individual half bridge is approximately 5 kHz, whereas the switching frequency of the resulting current curve is approximately 10 kHz.

Fig. 2 shows a further embodiment of a device according to the invention. In this exemplary embodiment, a load unit for a test stand is shown, which comprises a machine converter and a 3-phase electrical machine 1. The load unit is designed to test the mechanical drive train of a vehicle.

The machine converter corresponds to the exemplary embodiment according to FIG. 1a, with two half bridges 2, 2 ‘, 2a, 2a, 2b, 2b‘ being provided for each phase of the electrical machine 1, which are controlled separately via the control unit 3. In this exemplary embodiment, however, the electrical machine 1 is specially adapted to the machine converter and has two separate machine windings 5, 5, 5a, ba ‘, 5b, 5b‘ in each of its three phases U, V, W. These machine windings are brought out via the connections U + 1, U2, V1, Vz, W1, W2 and are connected to the outputs of the controlled half bridges 2, 2 ‘, 2a, 2a‘, 2b, 2b ‘. Since the machine windings for each phase are wound on a common iron core, there is no need to arrange additional interleaving chokes in this exemplary embodiment, since the machine windings take over their function.

Instead of a central machine converter, it can also be provided that each phase of the electrical machine 1 is controlled via a separate machine converter with several half-bridges, in the present exemplary embodiment two half-bridges in each case. This can be especially true for applications with very high powers

be beneficial.

Furthermore, it can be provided that, in the case of high-power electrical machines that have a plurality of windings per phase, these windings are brought out to separate machine converters, which are controlled via a common or separate, interconnected control units. For example, two separate machine converters can be provided for a machine with two windings on each phase, each of which supplies one of the windings on the phases.

The invention is not restricted to the present exemplary embodiments, but rather comprises all devices and methods within the scope of the following patent claims.

Terms used here, such as converter or machine converter, should not be interpreted too narrowly. A converter or machine converter according to the invention can be understood to mean any controlled electrical and / or electronic circuit which converts a direct voltage into an alternating voltage, or converts an alternating voltage into another alternating voltage. Such a circuit can be, for example, but not exclusively, a direct converter, a matrix converter, an AC voltage converter, a switched bridge inverter or the like. The specific circuit implementation of the converter is not essential. Converters provided according to the invention can also provide internal galvanic isolation and can be provided for high electrical powers, for example powers in the range of 100 kW with a direct voltage of 850 V or 300 kVA alternating current power.

List of reference symbols

1 Electric machine 2, 2 ‘, 2a, 2a‘, 2b, 2b ‘half bridge 3 Control unit

4, 4 ‘, 4a, 4a‘, 4b, 4b ° interleaving choke 5, 5 ‘, 5a, ba‘, 5b, 5b ‘machine windings

Claims (10)

Claims 1. Machine converter for supplying an N-phase electrical machine (1) with alternating current from a direct voltage source, for example a battery, a fuel cell or a direct voltage intermediate circuit, characterized in that - for at least one, preferably each of the N phases of the electrical Machine (1) M electronically controllable half bridges (2, 2 ‘, 2a, 2a‘, 2b, 2b ‘) are provided, where M is greater than one, - A control unit (3) controlling the half bridges (2, 2 ‘, 2a, 2a‘, 2b, 2b ‘) in pulse width modulation is provided, - The control unit (3) is designed to activate the half bridges (2, 2 ', 2a, 2a', 2b, 2b ') at least one, preferably each of the N phases with a time delay in such a way that the current of this phase is transferred to that of the Phase associated M half bridges (2, 2 ', 2a, 2a', 2b, 2b ') is divided essentially equally. 2. Machine converter according to claim 1, characterized in that the outputs of the M half bridges (2, 2 ', 2a, 2a', 2b, 2b '), which supply the same phase, via current-compensated interleaving chokes (4, 4 °, 4a , 4a ', 4b, 4b') are interconnected. 3. Machine converter according to claim 1 or 2, characterized in that the control unit (3) is designed to each of the M half-bridges (2, 2 ', 2a, 2a', 2b, 2b ') assigned to a phase for a substantially identical Activation duration ton and delayed to each other by a period of essentially ton / M. 4. Machine converter according to one of claims 1 to 3, characterized in that the number of phases N is equal to three. 5. Machine converter according to one of claims 1 to 5, characterized characterized in that the number M of half bridges (2, 2 ‘, 2a, 2a‘, 2b, 2b ‘) per phase is equal to two, three, four, five, six or higher, and / or that each of the Half bridges (2, 2 ‘, 2a‘, 2a ‘, 2b, 2b‘) include two controlled semiconductor switches Q1, Q2, preferably SiC transistors. 6. Load unit for a test stand, comprising a machine converter according to one of claims 1 to 5 and an N-phase electrical machine (1), characterized in that - in the electrical machine (1) in at least one, preferably in each of the N phases M separate and mutually insulated machine windings (5, 5 ', 5a, ba', 5b, 5b ') are provided, - The machine windings (5, 5 ‘, 5a, 5a, 5b, 5b‘) of this, preferably each phase in each case to one of the M half bridges (2, 2 ‘, 2a, 2a‘, 2b, 2b ‘) are led. 7. Drive unit of a vehicle, comprising a machine converter according to one of claims 1 to 5 and an N-phase electrical machine (1), characterized in that - in the electrical machine (1) in at least one, preferably in each of the N phases M separate and mutually insulated machine windings (5, 5 ', 5a, ba', 5b, 5b ') are provided, - The machine windings (5, 5 ‘, 5a, 5a, 5b, 5b‘) of this, preferably each phase in each case to one of the M half bridges (2, 2 ‘, 2a, 2a‘, 2b, 2b ‘) are led. 8. A method for supplying an N-phase electrical machine (1) with alternating current from a DC voltage source, for example a battery, a fuel cell or a DC voltage intermediate circuit, with M electronically controllable half bridges for at least one, preferably each of the N phases of the electrical machine (1) (2, 2 ', 2a, 2a', 2b, 2b ') are provided, and a control unit (3) controlling the half bridges (2, 2', 2a, 2a ', 2b, 2b') in pulse width modulation is provided, thereby characterized in that the control unit (3) activates the half bridges (2, 2 ', 2a, 2a', 2b, 2b ') at least one, preferably each phase, with a time delay in such a way that the current of these Phase on the M half bridges assigned to the phase (2, 2 ‘, 2a, 2a‘, 2b, 2b ‘) is divided essentially equally. 9. The method according to claim 8, characterized in that the control unit (3) the M half bridges of a phase (2, 2 ', 2a, 2a', 2b, 2b ') each for an identical duty cycle ton and each other by a period of ton / M delayed activated. 10. Use of a method according to one of claims 8 or 9 for operation a load unit of a test bench or a drive unit of a vehicle.