DE19851712A1 - Supplying switched reluctance, transversal flux machines with integral commutation, involves passing magnetic energy between windings with assistance from induced voltages - Google Patents

Abstract

The method involves using a self-controlled inverter with a DC intermediate circuit for excitation of unipolar stator currents, with an adjustable phase angle in the winding paths to the machine. The magnetic energy required to generate torque is passed on from one winding path to the next, with at least partial assistance from the voltages induced in the winding path by flux changes.

Description

The invention relates to a method for feeding reluctance and Transverse flux machines according to the preamble of claim 1.

From the comparison of advantages and disadvantages of synchronous machines it is known that the Reluctance machine is the simplest, cheapest and most trouble-free type of machine. There the performance of a reluctance machine is very different from the ratio of the Depends on inductivities in the longitudinal field and cross field direction of the rotor constructive measures a magnetically strongly asymmetrical structure of the active parts. In the past few years reluctance machines with changing magnetic Guiding values both in the rotor and in the stator, d. H. with "double-sided pole design" (double saliency) presented. These include the converter-powered variants, namely both the widespread switched reluctance machines as well Transverse flux machines.

In Fig. 1, the four-phase variants are shown in principle ( Fig. 1a axial section of a transverse flux machine, Fig. 1b sheet metal section of a reductance motor with 8 stator poles and 6 rotor poles).

There are a large number of converter circuit variants in the literature for supplying switched reluctance machines, which have different advantages and disadvantages depending on the converter topology and can only meet the requirements to a limited extent. Most of the time, on the way to minimizing the reactive power requirement of a machine and its converter expenditure or costs compared to the standard converter (standard: classic two-quadrant converter according to FIG. 2), losses in machine dynamics have to be accepted. The elaborate classic converter is the solution most often chosen in practice for machines with high utilization, especially with larger phase numbers <= 4. With a total of four valves (2 switches, mostly as IGBTs and two diodes) per line, it enables optimization of the switch-on and switch-off times to optimize performance and maximize the power yield by independently controlling individual lines.

Thus, a DC link capacitor C is _d in Fig. 2, the applies a voltage U _d of a two-quadrant converter single-stranded circuit in which from the intermediate circuit, a current i _z is flowing. Two IGBT switches S11, S12 or S21, S22 and two diodes D1, D2 or D3, D4 are provided per line. The converter works on an electrical machine, e.g. B. Reluctance machine, which is represented schematically by two phase windings (winding phases) L _{S1 (E)} L _{S2 (E)} and their rotationally induced voltages U _rot1 , U _{rot2, which} are electrically offset from one another by 180 °. String currents i ₁ , i _{2 which are} switched by the converter flow through the winding strands L _{S1 (E)} L _{S2 (E)} .

The aim of the solution according to the invention is to achieve these advantages with less to achieve complex circuit.

This solution according to the invention is characterized in claim 1.

This is a partial recovery of the magnetic energy in the DC intermediate circuit avoided, which reduces losses in the inverter and by means of the machine commutation directly into the subsequent winding conducted current to reduce the start of commutation in the Main branch valves of the inverter flowing current leads, so that the valve load (softer commutation) and the current steepness of the stator currents are reduced ("Harmonic Reduction").

Advantageous embodiments of the invention are in the remaining claims featured.  

The invention will be explained below with reference to the drawing figures 3 to 8. It demonstrate

FIGS. 3a and b show two variants of a double strand winding of an inverter, the process of the invention operates (hereinafter referred Kommutierungskonverter).

Fig. 4.1 waveforms of the phase voltage, current and inductance of the phase winding 2
for the circuit type: standard converter according to Fig. 2
a) without pre-ignition: 0 ° el.
b) with optimal pre-ignition angle: 80 ° el.

Fig. 4.2 waveforms of the phase voltage of winding phase 2 and the phase currents i1 and i2
for the circuit type: standard converter according to Fig. 2
a) without pre-ignition: 0 ° el.
b) with optimal pre-ignition angle: 80 ° el.

Fig. 5.1 waveforms of the phase voltage, current and inductance of the phase winding 2
for the circuit type: commutation converter according to Fig. 3a a) without pre-ignition: 0 ° el.
b) with optimal pre-ignition angle: 40 °.

Fig. 5.2 waveforms of the phase voltage of the phase winding 2 and the phase currents 1 and 2
for the circuit type: commutation converter according to Fig. 3a
a) without pre-ignition: 0 ° el.
b) with optimal pre-ignition angle: 40 ° el.

Fig. 6 shows the Kommutierungskonverter of FIG. 3a with a transformer Symmetrier-
(Circuit with soft commutation).

Fig. 7 shows the Kommutierungskonverter with a Kommutierungsbeschleuniger and reversing switch
(Circuit with accelerated commutation).

Fig. 8 shows the commutation converter with balancing transformer and commutation accelerator and reversing switch
(Switching with smooth accelerated commutation).

The circuit operating according to the method according to the invention (hereinafter referred to as the commutation converter) is characterized by the anti-parallel connection of two winding phases, which reduces the number of valves compared to the standard (see FIG. 2).

The designation of the circuit elements in FIG. 3 largely corresponds to that in FIG. 2, but in FIG. 3a only two diodes D1, D2 or in FIG. 3b a total of one diode D1 are provided per pair of strands.

Switching on a strand winding z. B. in motor operation is carried out by simultaneously closing two diagonally arranged switches (z. B. S11 and S12) in the inductance minimum of a strand winding. Once the current i1 has reached its end value, it can be kept at its setpoint after two different operating modes (by means of two-point control with an adjustable hysteresis). If the current i1 is too large, either both switches S11 and S12 (alternating clocks) or only one z. B. S12 (freewheel or single clock) opened. The current i1 decays faster with alternating clocking than with single clocking, because the inductance Ls1 discharges both against the DC link voltage and the machine voltage in the first case, in the second case it is switched to free-wheeling, which leads to lower current change speeds because only that Machine voltage is effective in a circle. Since this case results in a lower switching frequency under otherwise identical conditions and thus the losses are reduced, it is generally recommended to use single clocking. During the commutation from phase winding 1 (or 2 ) to phase winding 2 (or 1 ), the valve currents are also reduced by an additional freewheeling of the stator currents i1 (t), i2 (t) within the machine.

Switches S11 and S12 are opened to switch off phase windings. The commutation then starts largely from the switch-off time of the strand winding 1 (the strand winding 2 is initially de-energized, i2 (t) = 0) until the point of current equality (i1 (t) = u2 (t)) is machine-controlled, that is, from drives the voltage induced by rotation Urot1, Urot2, as long as all switches are open, as long as the freewheeling current in the following phase winding until the currents i1 and i2 are equal. It is irrelevant whether switches S21 and S22 are switched on immediately at the start of commutation or only later when the two winding windings are equal. At the time - the current equality, the switches S21 and S22 must be switched on at the latest so that the natural commutation, which has now ended, can be continued by the so-called forced commutation, otherwise a circulating current in both phase windings will result, which will result in the result Torque to zero and causes the machine to idle mechanically.

The anti-parallel connection of two phase windings of the machine offers the least favorable Failure of valves during operation the safety aspect to protect yourself Machine that works with the circuit described here for all circuit variants is guaranteed.

If the commutation phase from phase winding 1 to phase winding 2 is completed, the current in phase winding 2 is regulated to its final value in accordance with the above procedure. The current forms of the classic converter and commutation converter can be used for a characteristic comparison of the operating behavior. Figs. 4.1 and 4.2 show the time courses for a steady-state operating point for feeding of the machine by the conventional converter and Fig. 5.1 and 5.2, the corresponding current, voltage and Induktivitätszeitverläufe different by the Kommutierungskonverter at two Vorzündwinkeln. Here are the reactions of the free-running clocking by the flow of anti-parallel strand machine also in the falling edge of the current visible when Kommutierungskonverter (s. Fig. 5.2), but which hardly brings a deterioration of the operation with them. Rather, the current tail typical of the reluctance machines, which, as is well known, can also lead to negative moment formation, can be suppressed by additional measures described here. The magnetic energy of the current-carrying phase winding is thus partly passed directly into the following phase winding without loading the DC voltage intermediate circuit, which has fundamental advantages.

The valves and the DC link become more of the commutation reactive power relieves, which reduces losses.

In the following, supplementary and improvement options of the after Commutation converter operating according to the method are shown.

Since reluctance machines in the air gap have a strongly fluctuating inductance curve, different time constants of the branches involved are effective during commutation. This means for the Kommutierungskonverter of FIG. 3, for example during engine operation that in the commutating branch a residual current flows, even though the power in the neighboring branch aufkommutierende the target value has been reached. Since the residual current remains in the machine train after the change of sign of the inductance gradient leads to undesirable negative air gap moments that reduce the mean torque, different countermeasures are possible:

• I. Since the setting of an optimal pre-ignition angle to increase the torque and the total power factor for all converter variants for Reluctance machines is feasible, this is always the case with the following Assuming considerations. One can be used for the commutation converter Control measure to suppress the residual currents z. B. done so that a two-point control for the switched-on line at the earliest takes place when the current in the switched off winding commutation taking place has decayed to zero, d. H. if the switch is too current winding still remain switched on and the current there as long increases. This procedure involves additional valve loading and Torque ripple, especially at low speeds and rated current. This However, disadvantages are caused by higher machine voltages at high speeds strongly suppressed.
• II. A circuit-technical measure for suppressing the residual currents is provided by the use of a balancing transformer T (balancing voltages U ₁ , U ₂ ), which generates an additional commutation voltage as an inductive way and also makes this available to the neighboring string in a transformer ( FIG . 6). According to an initial estimate, this should have at least as large an inductance as the mean machine inductance so that the former is effective. The balancing transformer T is integrated in the two machine string windings in a cross connection so that the commutating branch receives a commutation voltage, the commutating current in the neighboring branch increasing more slowly in accordance with the increased branch inductance, which is why the choice of larger inductances is disadvantageous (L _transformer <2 × L _machine ). Here too, as with the previous variants, a higher torque yield is possible by setting the optimal pre-ignition angle. The rising and falling edges of the current, which typically run differently in reluctance machines, are thus symmetrized, with a "softer" commutation with the associated advantages being the result in each operating point.
• III. To increase the power factor, a commutation accelerator with a capacitor C _z for voltage amplification (U _c ) and an IGBT S _z including an inverse diode D _z for regenerative energy recovery and motor blocking for a double-strand circuit can be implemented ( FIG. 7). The accelerator must be designed for one strand winding pair, that is for the energy consumption of two phases, which can then contribute to a strong reduction in the reactive power requirement while avoiding negative torques. This supplementary variant is particularly recommended for engines with lower outputs.
• IV. The use of the combination of balancing transformer T and commutation accelerator to complete the commutation converter ( FIG. 8) leads to the best results in terms of the achievable mechanical performance and the total power factor with a correspondingly optimal pre-ignition.

Claims (8)

1. Method for supplying reluctance and transverse flux machines with and without additional excitation by means of a self-commutated inverter with a DC voltage intermediate circuit for generating unipolar stator currents with adjustable phase position in the winding strands of the machine, characterized by forwarding the magnetic energy required for torque generation from one winding strand to the next with at least partial support of the voltages induced by the flux change in the winding phase. 2. The method according to claim 1, characterized, that two current-carrying winding strands of the machine are connected in anti-parallel and thus be energized in the opposite direction. 3. The method according to claim 1 or 2, characterized, that as inductive consumers machines with an even number of phases <2, which consist of one or several winding strand pairs with 180 ° el. phase shift exist become. 4. The method according to any one of claims 1 to 3, characterized, that each two 180 ° el. offset machine winding strands as a load via two diodes connected anti-parallel and designed as a single or multiple double-strand circuit become.   5. The method according to any one of claims 1 to 4, characterized, that to support machine commutation one with the help of a balun in the commutating winding strands generated transformer Additional commutation voltage is coupled. 6. The method according to claim 5, characterized, that a single-phase balun (T) to generate the transformer Additional commutation voltages in series with the parallel winding strands the machine is switched with a phase rotation of 180 ° el. 7. The method according to any one of claims 1 to 6, characterized, that by a commutation accelerator consisting of a capacitor and a Switch incl. An inverse diode an additional voltage for simultaneous acceleration of the commutation process in two antiparallel connected winding strands becomes. 8. The method according to any one of claims 1 to 7, characterized, that the symmetry or commutation times caused by finite current steepness of the phase currents within a winding phase pair by setting one Preignition angle can be shortened.