GB2618204A - Lenz effect braking equaliser - Google Patents

Abstract

A device 3 to equalise the braking force experienced by a prime mover 1 when supplying rotational mechanical power to the shaft of an electrical generator 4 may comprise a compensator rotor (fig. 4) to compensate for the induction braking effect on the generator shaft. The compensator rotor may comprise six pairs of flux sources (S1-6) which may be magnets or fed inductors, the flux sources being positioned and electrically activated such that magnetic repulsion events on the flux sources occur at the precise time of the Lenz braking events occurring on the generator shaft. The device may be incorporated into existing wind turbine or hydroelectric equipment. The device may be applied to a generator driven by a modified DC electric motor which remains in speed-synchronism with that generator.

Description

Lenz Effect Braking Equaliser This invention relates to a means of increasing the efficiency of electrical power generation.

In 1834 the physician Emil Lenz gave his name to what is now more commonly known as Induction braking and since that time the assumption has been that any means to generate electricity with the use of magnetic fields moving close to inductors must include the mechanical effort to overcome that braking. This invention reverses that assumption.

Induction braking is the result of a magnetic field acting in a way to either repel or retard the movement of a generator's rotor. This invention provides the means to equalise that braking by fabricating and applying an opposing magnetic field, re-using only elements of the generator's output.

The equalisation mechanism compensates for the Lenz Effect braking on a generator's shaft and is therefore referred to as a "compensator" in the discussion below: Figure 1 shows how the compensator 3 is positioned between a prime mover land the generator 4 it serves. The output shaft of the compensator 6 is connected directly to the generator shaft. The input shaft of the compensator 7 is connected to the prime mover via a freewheel mechanism 2 which allows the compensator to independently increase the torque on the generator's shaft. Control 5 includes the rectification circuits.

The generator used is 3-phase. 6 sets of 360° full wave electrical cycles are delivered per physical revolution per phase.

Figure 2 shows the rectifier circuit applied to each individual generator phase. Each phase is treated separately. To accomplish equalisation, inductor components P1, P2, P3 and P4 are included.

hl and h2 are the paths of the two halfwaves per 360° cycle.

Figure 3 introduces the geometry of the compensator. Each 60° physical quadrant represents a 360° electrical full-wave +/-transition. P1, P2, P3 and P4 are fixed inductor sets, one per phase. The phases are labelled R, sand T. Each set is offset (from 0° electrical) by 120° as shown.

Figure 4 illustrates the construction of the compensator rotor. There are 6 pairs of flux sources (magnets or fed inductors) positioned so as to allow movement over both ends of the inductors.

Figure 5 illustrates the relationship between the affected halfwaves.

The re-use of each halfwave equalises the Lenz Effect braking occurring during the generation of the next. Assuming the halfwave is sinusoidal, current in P1 is delayed for 90° before being passed to P2. The rise in P2 peaks 180° after the peak of Pl.

Now, during the rise in P2 the second halfwave P3 is being generated starting its traversal of path h2.

As implied, the Lenz Effect braking is a step action occurring per halfwave at a natural angle (approx. 45°) along the axis of each halfwave generation.

Lenz Effect braking occurs during that second (P3) halfwave generation. This braking is equalised by arranging for the peak flux of P2 (prior halfwave) to repel one of the set of pairs of flux sources rotating on the compensator rotor. The radial position of the flux sources is adjusted to exactly match the radial position at which the Lenz braking is at its maximum.

This action is repeated for each halfwave due to the relative geometry between the compensator rotor and the fixed inductors. Consider the third inductor P3 in each set. The delayed current is passed to the fourth inductor P4. During this time the halfwave P1 (this time the first of the inductors in the set) is being generated and is experiencing a Lenz braking step action but again a compensating repel action occurs due to a rotor flux source being positioned exactly so as to be affected by a P4 repulse action on one of the pairs of flux sources mounted on the compensator rotor.

Figure 6 illustrates the per-phase sequence of compensation i.e., P2 compensates for P3, P1 compensates for P4 then the cycle continues. Any radial adjustment of the compensator rotor is common to all derived repulsions.

The inductors P2 and P4 (repelling) were originally the only inductors mounted and affecting the compensator rotor per phase. The inductors P1 and P3 were external. As an optimisation, by mounting P1 and P3, an additional pair of attraction operations were realised per halfwave per phase.

A practical note on the inductors P1, P2, P3 and P4: These are wound with copper of sufficient gauge to limit the resistance to only 0.20. To ensure maximum flux density, each has a ferrite core. The cores must be embedded to deal with the natural interaction between ferrite and flux sources. P1 attracts each source, so the natural ferrite attraction is supportive. When the magnet is positioned halfway over P1 & P2 the effect of the 2 cores is balanced out. As the magnet moves towards P2 the ferrite is supportive. At the point where P2 repels the source then, if not embedded, the ferrite in P2 would interfere with the repel action. What happens is that the inductor flux "masks" the natural attraction of the ferrite.

To recap on the action of the compensator, each phase of the generator is full wave rectified and a pair of inductors are wired in series on each branch of the rectifier circuit. The net effect is to introduce a current lag of 90° so the magnetic effect available as a force in the next inductor can be used to push the generator rotor over the Lenz braking which occurs during the next generated half wave. The effect on the output is to produce non-sinusoidal halfwaves whose area-under-the-curve has been increased. When wired in parallel the output is considerably enhanced DC power.

The overall action of the braking equaliser can be considered from a different perspective. The Lenz Effect is a force given by the equation 0 = BAcos 0 where B is the flux density, A is the area of application and 0 is the angle of application. For the generator components, B and A are relatively small in comparison to the compensator. The compensator provides timed and positioned repulsion events i.e., "step" acceleration events to match Lenz braking "step" events but the force used is greater than the braking force. This suggests that the extra torque noted in the tests below is the result of a magnetic force per halfwave derived from a small generator flux density and a larger compensator flux density. This in turn suggests that successively multiplied and aggregated magnetic force replaces mechanical force in the process of generating electrical power.

Refer to figure 1. The prime mover 1 is a 24V BLDC motor and the generator 4 is a 3-phase Permanent Magnet Generator (PMG).

Two test scenarios are presented here. The first involves only one phase and one set of inductors and illustrates the effect on speed when the compensator 3 is present. The second involves three phases and three sets of inductors and illustrates the resultant increase in torque.

Test Scenario 1-Single Phase Testing consists of a "before, after & compare" sequence and starts with the removal of the inductor set. The BLDC motor turns the shaft at 4 selected speeds and 2 sets of measurements are made at each. The first measurement is the simple DC (rectified) output of the "S" phase of the generator. The second is a mV value representative of the input power applied to the BLDC. 1mV = lx 24V = 24W.

These are the "uncompensated" results (no inductors present): Speed(rpm) V mV 250 8.6 2.3 500 18 7.5 750 27.2 15.2 1000 35 28 *** These are the "compensated" results: Speed(rpm) V mV 250 11 3.3 500 22.8 11.9 750 35 26.1 *** 1000 47 41 Note that the voltage reached at 1000 rpm in the uncompensated case is achieved at 750 rpm when compensated (marked ""*" above). This is, of course, for 1 phase only. In the final configuration, as there is one generator and 3 phases, there are 3 instances of added torque and therefore 3 instances of speed reduction.

The BLDC controller objects to extra torque because the shaft speed is reduced (u.) = P / T). The controller "sees" this as a mechanical brake.

If the prime mover was other than a standard electric motor then an increase in torque on the generator shaft would cause an increase in power out and a reduction in speed proportional to the magnitude x 3 of that torque. That reduction represents the reduction in power required to be supplied to the prime mover. In the case of the BLDC motor used in the prototype, the motor controller is designed to attempt to maintain a constant speed dependent upon the original power setting. Any reduction in shaft speed causes the controller to increase the power supplied to the motor. This does not apply to most other types of prime movers. As an example, the wind turbine relies on kinetic energy to rotational torque conversion and the application of that torque to a generator's shaft either directly or via a gearbox. Inserting a compensator between the source and the generator via a freewheel would allow the maintenance of that torque unhindered but with additional torque added by the compensator. The generator shaft speed reduces while the generator power increases in proportion to the torque applied by the attract and repel operations on the compensator rotor. This could have a knock-on effect for future builds in that smaller (hence less costly) turbines could be built having a power specification equal to existing larger machines. The compensator itself is a type of 3 phase motor running in a similar manner to the BLIDC but without the pulse width modulation requirement. As such it could run with the use of a derived 3-phase driver as input so a compensator could also be used as a prime mover.

Test Scenario 2-Phase "R", "S" and "T" Combined This test involves physically adding connected inductor sets into the compensator, noting differences as sets are added then calculating the increases in torque as a result.

Note. In this test only the inductor set "S" has a complete set of 4 inductors. "5" & "T" have only P1, P2 and P4 installed due to the build state at the time of test.

Uncompensated (all inductor sets are electrically connected but no set is physically mounted) 1000 rpm Vu = 48.3V lp = 35.2mV Phase "5" Inductor Set added.

1000 rpm Vs = 55.8V Ip = 50mV Note that the volts and the motor input power have increased. Increasing shaft torque is seen as a brake by the drive motor but at this point, the speed can be reduced so Vs = Vu: 850 rpm Vs = 48.3V lp = 37mV i.e., a speed reduction of 150 rpm Phases "5" & "R" Inductor Sets added.

1000 rpm Vrs = 58V lp = 55mV Similar scenario, reduce the speed so Vrs = Vu: 760 rpm Vrs = 48.3V lp = 37mV i.e., a speed reduction of 240 rpm Phases "5", "R" & "T" Inductor Sets added.

1000 rpm Vrst = 64V lp = 54mV Reduce the speed so Vrst = Vu 690 rpm Vrst = 48.3V lp = 36mV i.e., a speed reduction of 310 rpm Calculation of the Torque Advantage T = P / w, therefore Uncompensated Torque: w = 21-cf = 271 (1000/60) = 104.73 rad/ I = V/R = 48.3 / 5 = 9.66A P = VI = 48.3 x 9.66 = 466W T = P / w = 466 / 104.73 = 4.449 Nm/s Compensated Torque with Inductor Sets R S & T installed: w = 2nf = 2m (690/60) = 72.26 rad/s I = V/R = 48.3 / 5 = 9.66A P = VI = 48.3 x 9.66 = 466W T = P / CO = 466 / 72.26 = 6.44 Nm/s Only inductor set "5" has a full set of coils installed. This explains the reduction in speed of 150rpm as compared with the other sets at 130rpm.

Note also, as the sets are loaded, the BLDC controller detects greater braking and works against the compensation. However, if this were not the case then the total speed reduction would be 130 + 150 + 130 = 410 rpm.

In that case, w = 2m ((1000-410)/60) = 61.7 rad/s T = 466 / 61.7 = 7.55 Nm/s, a torque increase of 70% Furthermore, if all 3 inductor sets had a full set of coils installed the total speed reduction would be 3 x 150 = 450 rpm.

In that case, w = 2m (550/60) = 57.27 rad/s T = 466 / 57.27 = 8.14 Nm/s a torque increase of 83%.

Applications In the test section above it has been noted that the BLDC motor in use acts in a similar manner to any electrical motor in that if a reduction in shaft speed is detected it assumes that a brake force is being applied and responds with extra consumed power to attempt to maintain the original speed. Currently in progress is the build of a drive motor whose speed is forced to remain in synchronism with the generator in use. Only an increase in output torque occurs with an increase in input power to the motor.

Therefore, one application for this device could be that of enhancing any DC source of electrical power. This would include power enhancement of renewable devices such as PV or hydro.

In an associated manner the device could be used in a stand-alone charger situation in that the braking equaliser could be driven by a battery which in turn received the result of the increase in power due to the increase in torque as seen in Test Scenario 2 above. If this was to be applied in a domestic situation where the battery was replaced by a battery bank, then the possibility of domestic off-grid electrical supplies could be a reality. EV charging could also be affected. As could the efficiency of the generation of Green Hydrogen.

Claims (4)

1. Lenz Effect Braking EqualiserCLAIMS1. A means of replacing mechanical force applied to a generator's shaft with a force derived from successively multiplied and aggregated magnetic force.
2. 2. A device according to claim 1 which, in the case of rotary electrical generators, challenges the assumption that, since 1834, only mechanical force could be used to equalise what is now commonly referred to as Induction Braking (the Lenz Effect).
3. 3. A device according to claim 1 that arranges to recycle the electrical output of a generator prior to dissipation in a load.
4. 4. A device according to claim 1 that momentarily delays each generated electrical halfwave supplied by a generator, converts it to a magnetic field then applies the magnetic force of that field, precisely timed and positioned, to accelerate flux sources attached to that generator's shaft.