METHOD FOR DETERMINING THE STATIC DELIVERY HEIGHT OF A PUMP

Description

[0001] The invention relates to a method for determining the static delivery head of a speed-controlled centrifugal pump unit in an open hydraulic system.

[0002] When a fluid is pumped from a first container to a second container that is located at a higher elevation, a portion of the pressure applied by the centrifugal pump is required to overcome the height difference between the containers, specifically the difference between the liquid level in the first container (suction-side liquid level) and the liquid level in the second container (suction-side liquid level). This height difference is called the geodetic head. In closed hydraulic systems, such as heating or cooling circuits, the geodetic head is zero. Only when the height difference has been overcome, i.e., when the differential pressure Δp applied by the pump corresponds to a delivery head H (H = Δp / (ρ·g)) that exceeds the geodetic head, is the flow rate greater than zero.

[0003] Such a geodetic height also exists, for example, in the wastewater sector when wastewater from a pump sump is to be discharged via a pressure line into a higher-lying sewer line. In this case, the geodetic height Hgeo is the difference in height between the level in the pump sump and the height of the transition from the pressure line to the sewer line, as described, for example, in German patent application DE 10 2014 006 828 A1. Figure 1 This is shown. In the case of a borehole pump, the geodetic height would be the difference in height from the groundwater level to the surface.

[0004] If the first and second tanks are closed and a pressure difference exists between them, this system-related pressure difference must also be overcome by the pump to achieve a flow rate greater than zero. The sum of the geodetic head Hgeo and the system-related pressure difference between the pressure and suction sides of the pump (which also exists when the pump is switched off) constitutes the static head Hstatic. This is expressed by the following equation: H static = p out − p in ρ ⋅ g + H geo in the H static the static delivery head p out the pressure-side pressure / pressure in the second container p in the suction-side pressure / pressure in the first container ρ The density of the pumped fluid g is the acceleration due to gravity (9.81m / s 2< ) and H is the geodetic height.

[0005] The static head (Hstatic) is therefore the head (Hstatic) of the centrifugal pump unit that must be overcome to obtain a flow rate (Q). Since it depends on at least one variable water level, the static head (Hstatic) is also variable. Thus, the static head (Hstatic) increases when the water level in the first reservoir drops. A static head also exists in drinking water supply networks that are already supplied by the water supplier. Booster pumps (pressure booster systems) are used here to increase the supply pressure and ensure sufficient flow pressure at the highest and most distant taps. Due to the supply pressure, the static head initially appears negative here, depending on the measuring point.A drinking water supply system is also an open hydraulic system because it is open to the water supplier and the taps can be opened to the atmosphere. Furthermore, it is not intended to circulate water continuously in a closed loop.

[0006] In the representation of the system curve 1 of the hydraulic system, which describes the relationship between the delivery head H and the delivery flow Q in the so-called HQ diagram of the pump, the static delivery head Hstatic (Q=0) is shown as an upward shift of the pipe network parabola (Q>0, flow-dependent delivery head) on the pressure axis of the HQ diagram, as shown in Figure 1 The line is shown, or, in the case of a pressurized drinking water supply network, it runs downwards. In each case, the pipe network parabola does not pass through the origin.

[0007] Modern control systems for centrifugal pump units require precise knowledge of the pump's operating point B for maximum efficiency. This point lies at the intersection of the pump curve 2 (present at the current operating speed) and the system characteristic curve 1. Determining the operating point B in open hydraulic systems requires not only the slope of the pipe network parabola (i.e., the varying pipe resistance due to changing valve positions) but also the static head Hstatic, as it forms part of the system characteristic curve 1. Therefore, knowing the static head Hstatic is essential. This is straightforward if it can be derived from the system's design data. Otherwise, it must be determined.

[0008] European patent application EP 1 072 795 A1 discloses a method for traversing the entire operating curve of a system by varying the rotational speed and measuring the flow rate, delivery head, and / or power output. This process also determines the static delivery head. A disadvantage of this method is the requirement for sensors. Furthermore, the determination of the operating curve is not performed during normal operation, but rather in a separate investigation process in which normal operation is interrupted or suspended. Consequently, to determine the static delivery head, the operating point of the centrifugal pump unit intended for normal operation is deviated from.

[0009] European patent EP 2 610 693 B1 describes a method for optimizing the energy efficiency of a pump system, which includes a system identification phase in which the changing static head is also determined. For this purpose, the pump system is operated at its two limiting cases of maximum and minimum water levels to determine the minimum and maximum static head. Thus, the determination of the system curve is not performed during normal operation, but rather in a preceding system identification phase. To determine the static head, the operating point of the centrifugal pump unit is also significantly altered.

[0010] Other prior art documents relevant to the invention are US 2014 / 136000 A1 and EP 2 354 556 A1.

[0011] The object of the present invention is to overcome the aforementioned disadvantages and to provide a method and a centrifugal pump unit executing this method in which the determination of the static delivery head is carried out continuously at the current operating point without affecting the ongoing operation of the centrifugal pump, and in particular, sensors for the delivery flow and the delivery head are to be dispensed with.

[0012] This problem is solved by a method having the features of claim 1 and a centrifugal pump according to claim 12. Advantageous embodiments are specified in the dependent claims and are explained below.

[0013] According to the invention, it is provided that in the method for determining the static delivery head H static of a speed-controlled centrifugal pump unit operated at an operating point B in an open hydraulic system, the delivery head H of the centrifugal pump unit at this operating point B is modulated with an excitation frequency fg which is so low that a flow rate fluctuation ΔQ is caused, in particular without phase shift between the flow rate (Q) and the delivery head (H), wherein modulation parameters H 0 , Q 0 , H 1 , Q 1 are determined from the flow rate fluctuation ΔH and the flow rate fluctuation ΔQ, using which the static delivery head H static is determined.

[0014] The particular advantage of this method is that the static delivery head Hstatic can be determined during the normal operation of the centrifugal pump unit, in which the current operating point B exists. The operating point B is not deviated from on average, and no separate system identification process takes place outside of normal operation.

[0015] The method can be used in all open hydraulic systems, where "open" is understood to mean that the hydraulic system does not form, or at least not only forms, a closed circuit in which the pumped medium simply circulates. The hydraulic system could be, for example, a borehole pump with a connected pressure line, a wastewater pumping station with a connected pressure line, a drinking water supply network, or any other pipeline network in which the centrifugal pump operates and which has a static head, as is inherent in open hydraulic systems.

[0016] Modulation of the delivery head can be achieved, for example, by modulating the rotational speed N(t). This can be accomplished by applying a periodic excitation signal Fg(t) with an excitation frequency fg to a setpoint value for the operating speed N0 present at operating point B: N t = N 0 + N 1 ⋅ F g t .

[0017] Preferably, the excitation signal Fg(t) is a sine wave signal Fg(t) = sin(2πfg·t). The modulation amplitude N1 can be between 1% and 10% of the current operating speed or rated speed of the pump, or between 10 rpm and 100 rpm.

[0018] In the case of torque control, it is alternatively possible to achieve the modulation of the delivery head by applying the operating torque present at operating point B.

[0019] The excitation frequency fg should be chosen so low that the pumped or to-be-pumped fluid, despite its inertia, can follow the periodic fluctuation. This naturally depends on the inertia or the total volume of fluid to be set in motion. It has been shown that an excitation frequency fg of less than 1 Hz is suitable for hydraulic systems with a comparatively small fluid volume. Preferably, the excitation frequency fg is less than 0.5 Hz. At the same time, the excitation frequency fg should not be too low so that the system can be considered quasi-stationary, changes to the hydraulic system, e.g., by opening or closing taps, have a minimal impact, and detection does not take too long. It has been shown that an excitation frequency fg above 0.05 Hz, particularly around 0.1 Hz, is ideal.

[0020] Preferably, the static head is determined using an equation describing the hydraulic system's curve. This equation specifies the head H required for a given flow rate Q and includes a quadratic term whose coefficient represents the system's hydraulic resistance R. Determining the static head via the hydraulic curve is straightforward. This is particularly simple if the equation contains only the quadratic term and a flow rate-independent term (i.e., no linear term) that specifies the static head Hstatic, as no further parameter needs to be determined in this case.

[0021] At least some of the modulation parameters can be used to determine the hydraulic resistance R.

[0022] Suitablely, the determined modulation parameters are the respective DC component H 0 , Q 0 of the delivery head H and the delivery flow Q and the respective amplitude H 1 , Q 1 of the delivery head variation ΔH and the delivery flow variation ΔQ.

[0023] The DC components H0 and Q0 are the mean values ​​around which the delivery head H and the delivery flow rate Q, respectively, fluctuate. Thus, the DC component H0 of the delivery head H is the average delivery head H present during the process. Furthermore, the DC component Q0 of the delivery flow rate Q is the average delivery flow rate Q present during the process. Together, these two DC components H0 and Q0 define the operating point in the HQ diagram.

[0024] For example, the DC component H₀ of the delivery head H can be determined by integrating the delivery head H over at least one period, and / or the DC component Q₀ of the delivery flow Q can be determined by integrating the delivery flow Q over at least one period. The DC components thus each represent the arithmetic mean of the delivery head H or the delivery flow Q, respectively. Therefore, the DC components H₀ and Q₀ can be calculated mathematically as follows: H 0 = ∫ 0 T H t dt Q 0 = ∫ 0 T Q t dt

[0025] The required delivery head H(t) and flow rate Q(t) for integration can be continuously determined in various ways, for example, using measurement technology. The differential pressure can be measured using one or two sensors, and the delivery head can be calculated from this. Alternatively, a volumetric flow sensor can be used to measure the flow rate. To avoid using sensors, the flow rate and delivery head can be determined purely computationally.

[0026] For example, the method described in European patent application EP 3123033 A1 can be used, which exploits the hydraulic impedance of the system by modulating the delivery head and determining the flow rate from the resulting system response, which manifests itself, for example, in the fluctuation of the electrical power consumption, by evaluating at least one sinusoidal integral of the system response, similar to a Fourier transform. For further details, please refer to EP 3123033 A1. From the generally known physical-mathematical relationship between flow rate Q and delivery head H at the pump unit, the delivery head H can then be determined, thus establishing the hydraulic operating point B(Q, H) of the pump unit.This determination method can be combined particularly easily and effectively with the inventive method for determining the static delivery head if the excitation frequency used there is higher, in particular by more than a factor of 10, than the frequency used in the inventive method. For example, the excitation frequency for determining the delivery flow can be between 1 Hz and 20 Hz, preferably at approximately 5 Hz.

[0027] According to another alternative, the flow rate and delivery height can be determined using a model-based observer. Such a method is described, for example, in Luxembourg application LU501040 dated 17.12.2021.

[0028] The amplitude H1 of the delivery head variation ΔH and the amplitude Q1 of the delivery flow variation ΔQ define the range of variation of the delivery head H and the delivery flow Q. Mathematically, they correspond to half the difference between the maximum and minimum values ​​of the delivery head H and the delivery flow Q, respectively, making their calculation straightforward.

[0029] Taking into account a phase shift ϕ 1 of the delivery head or delivery flow fluctuation to the excitation signal (rotational speed fluctuation), which is present in the case of an insufficiently small excitation frequency, the delivery head fluctuation ΔH and the delivery flow fluctuation ΔQ can be expressed as complex-valued alternating quantities. X 1 ¯ = X 1 e j 2 πf g t + φ = X 1 cos 2 πf g t + φ + j sin 2 πf g t + φ The calculations are considered as follows: X 1 ¯ = X 1 , cos + j X 1 , sin with X 1 , sin = ∫ 0 T X t ⋅ sin 2 πf g dt und X 1 , cos = ∫ 0 T X t ⋅ cos 2 πf g dt

[0030] The amplitude X 1 of the alternating quantity X 1 is X 1 = X 1 , cos 2 + X 1 , sin 2 and the phase φ 1 = arctan X 1 , sin X 1 , cos .

[0031] However, if there is no phase shift ϕ₁ or a negligibly small one, the amplitude H₁ of the delivery head fluctuation ΔH can be determined directly by integrating the product of the delivery head H and a sine or cosine signal with excitation frequency fg over at least one period, and / or the amplitude Q₁ of the delivery flow fluctuation ΔQ can be determined directly by integrating the product of the delivery flow H and a sine or cosine signal with excitation frequency fg over at least one period T. Thus, the amplitudes H₁ and Q₁ can be calculated mathematically as follows: H 1 = ∫ 0 T H t ⋅ sin 2 πf g   dt Q 1 = ∫ 0 T Q t ⋅ sin 2 πf g dt

[0032] Using the amplitude H₁, Q₁ of the delivery head variation ΔH and the delivery flow variation ΔQ, as well as the DC component Q₀ of the delivery flow Q, the current hydraulic resistance R of the system can be determined. The current hydraulic resistance R is the slope of the system curve at the given operating point. It can then be used to determine the static delivery head H₁ static using the equation describing the system curve of the hydraulic system.

[0033] Preferably, the hydraulic resistance R of the system is determined according to the equation R h = H 1 Q 1 ⋅ 2 Q 0 , in der R h is the hydraulic resistance, H 1 is the amplitude of the delivery head fluctuation ΔH, Q 1 is the amplitude of the delivery flow fluctuation ΔQ and Q 0 is the DC component of the delivery flow Q.

[0034] Determining the static head Hstatic is particularly simple using the hydraulic curve of the system, since its basic shape is known and the operating point B(H0, Q0), whose coordinates correspond to the two previously mentioned DC components, lies on it. Advantageously, a quadratic equation of the form H = R·Q2 + Hstatic can be used as the system curve, because this describes the physics with good accuracy and only has the parameter R, which describes the slope of the curve or the previously calculated hydraulic resistance. This curve thus makes it possible to determine the static head Hstatic using the DC components H0, Q0 of the head H and the flow rate Q, and the hydraulic resistance of the system.

[0035] This can be done by determining the static delivery head H static according to the equation H static = H 0 − R h ⋅ Q 0 2 is determined in the H static is the static delivery head, H 0 is the DC component of the delivery head H, Q 0 is the DC component of the delivery flow Q and R h is the hydraulic resistance of the system.

[0036] The invention further relates to a speed-controlled centrifugal pump unit comprising a centrifugal pump, an electric motor driving the pump, and pump electronics for controlling and / or regulating the electric motor, wherein the pump electronics are configured to carry out the method according to the invention. The pump electronics suitably include a frequency converter and speed and / or torque control.

[0037] Further features, properties, effects, and advantages of the invention are explained in more detail below with reference to exemplary embodiments and the accompanying figures. The reference numerals in the figures retain their meaning from figure to figure. In the figures, reference numerals always denote the same or equivalent components, areas, directions, or locations.

[0038] It should be noted that, within the context of this description, the terms "exhibit," "comprise," or "include" in no way exclude the presence of other characteristics. Furthermore, the use of the indefinite article for an object does not preclude its plural form. This shows: Figure 1: HQ diagram with a pump characteristic curve 2 and a system curve 1, which includes a static head drop H static. Figure 2: HQ diagram according to Figure 1with a rapid delivery head modulation compared to the inertia of the conveyed fluid Figure 3: HQ diagram according to Figure 1 Figure 4: HQ diagram with a pump characteristic curve 2 and a system curve 1, which includes a static drop in delivery head H static, and illustration of a fluctuation around the operating point B of the centrifugal pump located at the intersection of the curves. Figure 5: Representation of a speed variation with DC component N 0 and amplitude N 1 and the resulting flow rate variation ΔQ with DC component Q 0, the amplitude Q 1 and the phase shift ϕQ 1 related to the speed excitation over time t. Figure 6: A flow diagram of the method according to the invention.

[0039] Figure 1Figure 1 shows an HQ diagram with a system curve 1 of a hydraulic system with a positive static head Hstatic. System curve 1 describes the physical relationship between the head H and the flow rate Q and thus indicates the required head H, or rather the differential pressure Δp proportional to the head H that a centrifugal pump unit must generate in the hydraulic system to obtain a specific flow rate Q. The static head Hstatic is the minimum head that must be achieved to ensure a flow rate greater than zero. If there is no inherent pressure difference between the suction and discharge sides of the centrifugal pump unit, the static head corresponds to the geodetic head. System curve 1 can be mathematically simplified by the equation H(Q) = Rh · Q2 + Hstatic.

[0040] In the HQ diagram of Figure 1Furthermore, a pump curve 2 is shown. For a constant operating speed N 0, it describes the physical relationship between the delivery head H and the flow rate Q at the centrifugal pump unit. The operating point B established during operation of the centrifugal pump unit at the operating speed N 0 lies at the intersection of pump curve 2 with the system curve 1, i.e., the combination of the geodetic head H static and the delivery head drop HR (Q) = R h ·Q 2< , which is caused by the hydraulic resistance R of the pipe network (see also Figure 4 ).

[0041] If a sinusoidal signal FA is applied to the delivery head H at operating point B, and its excitation frequency f A is chosen to be so high that the hydraulic system cannot follow the resulting delivery head modulation due to the inertia of the pumped fluid, for example, water, the flow rate Q remains essentially constant, and only a delivery head fluctuation ΔH occurs. The operating point B therefore changes parallel to the pressure axis, i.e., vertically, for Q ≈ constant. Thus, a rapid delivery head modulation occurs relative to the inertia of the pumped fluid. This is in Figure 2 As shown, such modulation can be used to determine the flow rate Q without sensors, as described in European patent application EP 3123033 A1. The frequency f A (excitation frequency) can be between 1 Hz and 20 Hz, for example at approximately 5 Hz.

[0042] In contrast, in the inventive method for determining the static delivery head Hstatic, a different sinusoidal signal Fg(t) is superimposed on the delivery head H at operating point B, the frequency of which fg is chosen to be so low that the hydraulic system can follow this excitation without any significant phase shift. In this case, the operating points B no longer run vertically, but on or along the pipe network parabola, as is the case with this Figure 3 To illustrate: For example, the frequency fg of this sinusoidal signal Fg is between fg = 1 Hz and 0.05 Hz, for example, approximately 0.1 Hz. In the latter case, the frequencies fg = 0.1 Hz and fA = 5 Hz differ by a factor of 50.

[0043] The periodic change of the delivery head H (modulation) is achieved by superimposing the excitation signal F g (t) on the target speed N 0 required to reach the operating point B within the speed control of the centrifugal pump unit, so that the actual speed N(t) is represented as follows: N t = N 0 + F g t = N 0 + N 1 sin 2 π f g ⋅ t

[0044] The excitation signal Fg(t) has the excitation frequency fg of, for example, 0.1 Hz and an excitation amplitude N1 of, for example, 10 to 50 rpm. The actual speed N(t) therefore fluctuates between a minimum value Nmin = N0 - N1 and a maximum value Nmax = N0 + N1, so that the pump curve 2 rises and falls. This is in Figure 4 This illustrates that the operating point B(H 0 ,Q 0 ) moves along the system curve 1, causing a delivery head fluctuation ΔH (pressure fluctuation) on the one hand and a delivery flow fluctuation ΔQ on the other.

[0045] To illustrate the time course 3 of the low-frequency rotational speed excitation and the resulting flow rate fluctuation ΔQ, the time course of the rotational speed N(t) and the time course of the flow rate Q(t) are shown in Figure 5 This is illustrated. When the speed is varied, the operating speed is a DC component corresponding to the unmodulated target speed N0, superimposed by the excitation amplitude N1. The time course 4 of the resulting flow rate variation ΔQ has the DC component Q0, the amplitude Q1, and a phase shift ϕQ1 relative to the speed excitation. Analogously, the delivery head variation ΔH could also be represented in a diagram with the DC component H0, the amplitude H1, and the phase shift ϕH1 relative to the speed excitation. Ideally, the speed excitation is chosen to be so low-frequency that the phase shift ϕQ1 is zero.

[0046] Due to their periodic fluctuations, the delivery head and delivery flow rate are now alternating quantities. Their alternating component, i.e., ΔQ = Q₁ · sin(2πf g + ϕ Q₁ ) and ΔH = H₁ · sin(2πf g + ϕ H₁ ), can, as is common in electrical engineering, be considered as a complex number, consisting of a real part and an imaginary part with the imaginary unit j, and comprising the magnitude Q₁, H₁ and the phase ϕ Q₁, ϕ H₁. If the delivery flow rate fluctuation ΔQ and the delivery head fluctuation ΔH are each represented as complex numbers... Q 1 , H 1 as follows: Q _ 1 = Q 1 cos φ Q 1 + jsin φ Q 1 und H _ 1 = H 1 cos φ H 1 + jsin φ H 1 , For a hydraulic system, a complex-valued hydraulic impedance can be used, analogous to an electrical impedance. Z h = Z h ( cos(ϕ Zh ) + jsin(ϕ Zh )) are defined by the quotient of the delivery head variation ΔH and the delivery flow variation ΔQ, more precisely their complex amplitudes H 1, Q 1 is formed: Z _ h = H _ 1 Q _ 1 = Z h cos φ Zh + jsin φ Zh

[0047] The hydraulic impedance thus describes the relationship between the excitation-induced delivery head amplitude H 1 and the resulting delivery flow amplitude Q 1, which depends on the differential resistance R' h and the hydraulic inductance L h of the system or pipe network as well as the excitation frequency fg: Z _ h = H _ 1 Q _ 1 = R h ′ + j 2 πf g L h

[0048] The differential resistance R h ′ corresponds to the real part of the hydraulic impedance Z h and can therefore also be determined by the amplitudes H1 and Q1 and the phase angles ϕH1 and ϕQ1 of the delivery head and delivery flow fluctuations are described and consequently can also be calculated from them: R h ′ = Z h cos φ Zh = H 1 Q 1 cos φ H 1 − φ Q 1

[0049] The differential resistance R h ′ This represents the linearized relationship between the delivery head H and the delivery flow Q for operating point B with the DC components Q 0 and H 0 of the delivery flow Q and the delivery head H of the equation of the system curve 1, which contains the non-differential resistance R h: H 0 = R h · Q 0 2< . Thus, the following relationship between the resistance R h and the differential resistance results. R h ′ : R h ′ = 2 R h Q 0 = H 1 Q 1 cos φ H 1 − φ Q 1

[0050] Thus, if the DC component Q 0 of the delivery flow Q is known, the "normal" resistance R h can be calculated using the amplitudes H 1 and Q 1 and the phase angles ϕ H1 and ϕ Q1 of the delivery head H and the delivery flow Q: R h = 1 2 Q 0 ⋅ H 1 Q 1 cos φ H 1 − φ Q 1

[0051] Because of the low-frequency excitation at frequency fg, the flow rate and delivery head fluctuations are almost synchronous ( ϕ H1 ≈ ϕ Q 1), is the expression cos( ϕ H 1 - ϕ Q1) is approximately equal to 1. Therefore, the above calculation rule for the hydraulic resistance R h can be simplified to R h ≈ H 1 Q 1 2 Q 0

[0052] This simplification is also advantageous because an exact calculation of the hydraulic resistance Rh would require the phase angles ϕH1 and ϕQ1. However, if these are slightly inaccurate due to disturbances, a significant error results in the value for the hydraulic resistance Rh.

[0053] After the hydraulic resistance R h of the system or pipe network has been determined using equation 16 or 17, the static delivery head H static can be calculated from the system curve 1 using the DC components H 0 ,Q 0 for the delivery head H and the flow rate Q, which form the pair of values ​​for the delivery head H and the flow rate Q present at operating point B, as follows: H static = H 0 − R h Q 0 2 + 1 2 Q 1 2

[0054] In the case that the amplitude Q1 of the flow rate fluctuation ΔQ is much smaller than the flow rate Q0 present at operating point B, the above equation can be further simplified to: H static ≈ H 0 − R h Q 0 2

[0055] In light of the foregoing, the inventive method for determining the static delivery head H static can be comprised of the following process steps, which are described in Figure 6 Illustrated are: S1: Generation of a delivery height modulation

[0056] In a first step S1, the delivery head H of the centrifugal pump unit at operating point B is modulated with an excitation frequency fg to maintain a delivery head fluctuation ΔH, whereby the excitation frequency fg is so low that a flow rate fluctuation ΔQ is also induced. Preferably, the modulation is achieved by applying an excitation signal Fg(t) with the aforementioned excitation frequency fg to the target speed N0 of a speed control system present at operating point B. This frequency can, for example, be fg = 0.1 Hz. In the case of torque control, the target torque to be set can also be applied with a corresponding excitation signal. S2: Determination of delivery head and flow rate

[0057] In a second step S2, the delivery height H and the delivery flow rate Q are continuously determined. This can be done by measurement using appropriate sensors or by calculation.

[0058] The calculation can be performed, for example, by additionally modulating the delivery head or rotational speed with a periodic excitation signal whose excitation frequency fA is at least ten times higher than the first excitation frequency fg, so that this second modulation does not significantly affect the flow rate due to the inertia of the pumped fluid. The system response is then evaluated, for example, in the form of the electrical power consumption of the centrifugal pump unit, by calculating a sine integral from it and then calculating the flow rate Q from the integral value using a table or equation to calculate the flow rate, as described in EP 3123033 A1. The delivery head H can then be calculated from the flow rate Q.

[0059] Alternatively, the calculation can be carried out using a mathematical model of the centrifugal pump in the hydraulic system, e.g. in the form of a control-engineering observer, as described, for example, in the Luxembourg application LU501040. S3: Amplitude determination

[0060] In a third step S3, the amplitudes Q1 and H1 of the delivery head variation ΔH and the delivery flow variation ΔQ are determined. The amplitudes Q1 and H1 constitute the first modulation parameters to be determined. For this purpose, in a first sub-step S3a, the amplitude Q1 of the delivery flow variation ΔQ can be determined by integrating the product of the determined delivery flow Q and a sinusoidal signal with excitation frequency fA over at least one period of the excitation signal FA(t). In a second sub-step S3b, the amplitude H1 of the delivery head variation ΔH can be determined in the same way by integrating the product of the determined delivery head H and a sinusoidal signal with excitation frequency fA over at least one period of the excitation signal FA(t). The two sub-steps S3a and S3b can also be interchanged. S4: Determination of operating point

[0061] In a fourth step, S4, the DC components Q0 and H0 of the delivery head H and the delivery flow Q are determined. These DC components Q0 and H0 constitute the second modulation parameter to be determined. In the HQ diagram, they represent the pair of values ​​defining the operating point B on the system curve 1, so that the operating point is determined by calculating the DC components Q0 and H0. For this purpose, in a first sub-step, S4a, the DC component Q0 of the delivery flow Q can be determined by integrating the determined delivery flow Q over at least one period of the excitation signal FA(t). In a second sub-step, S4b, the DC component H0 of the delivery head H can be determined in the same way by integrating the determined delivery head H over at least one period of the excitation signal FA(t). The two sub-steps, S4a and S4b, can also be interchanged.

[0062] Steps S3 and S4 can also be performed in reverse order. S5: Resistance determination

[0063] In a fifth step S5, the current hydraulic resistance R h of the system or pipe network is determined. This is done using the determined amplitudes Q 1 , H 1 of the delivery head fluctuation ΔH and the delivery flow fluctuation ΔQ as well as the determined DC component Q 0 of the delivery flow Q by evaluating the above equation 17, provided that the excitation frequency is so low that the delivery head fluctuation ΔH and the delivery flow fluctuation ΔQ are in phase.

[0064] If this is not the case, the phase angle can also be considered. ϕ H1 and / or ϕ Q 1. shall be determined as follows: H 1 , sin = ∫ 0 T H t ⋅ sin 2 πf g dt H 1 , cos = ∫ 0 T H t ⋅ cos 2 πf g dt Q 1 , sin = ∫ 0 T Q t ⋅ sin 2 πf g dt Q 1 , cos = ∫ 0 T Q t ⋅ cos 2 πf g dt where: φ H 1 = arctan H 1 , cos H 1 , sin φ Q 1 = arctan Q 1 , cos Q 1 , sin

[0065] Note that the H 1,sin or Q 1,sin term appears in the denominator here, since the excitation was defined as a sine function. Using the phase angle and equation 16, the resistance R h can then be calculated. S6: Determination of the static delivery head

[0066] In a sixth step S6, the desired static delivery head Hstatic is finally determined. This is done at least using the determined DC components Q0, H0 of the delivery head variation ΔH and the flow rate variation ΔQ, i.e., the operating point B, as well as using the determined hydraulic resistance Rh by evaluating one of the aforementioned equations 18 or 19, preferably equation 19. If the determination of the static delivery head Hstatic is to be carried out using equation 18, the amplitude Q1 of the flow rate variation ΔQ is used in addition to the aforementioned quantities.

[0067] The described method is executed by the centrifugal pump unit, in whose pump electronics it is implemented. For this purpose, the pump electronics have at least one processor and a programmable, non-volatile memory module in which a control program with instructions is stored, the execution of which on the processor causes the implementation of the method according to the invention in the pump electronics and thus in the centrifugal pump unit.

[0068] The pump electronics include First, means for generating a delivery head modulation, specifically designed for performing step S1. Second, means for determining the delivery head and flow rate, specifically designed for performing step S2. Third, means for determining the amplitudes of the delivery head and flow rate fluctuations, specifically designed for performing step S3. Fourth, means for determining the current operating point of the centrifugal pump unit, specifically designed for performing step S4. Fifth, means for determining the current hydraulic resistance Rh of the system or pipe network, specifically designed for performing step S5. Sixth, means for determining the desired static delivery head Hstatic of the system, specifically designed for performing step S6.

[0069] The first means of generating the delivery head modulation act on a speed control or torque control, which is also part of the pump electronics, by specifying a setpoint that changes with the excitation frequency fg. This setpoint is superimposed on the setpoint N0 for the current operating point, which can, for example, originate from a higher-level characteristic curve control. To achieve the modulating setpoint, the speed control or torque control operates a frequency converter, which is also part of the pump electronics, to adjust the corresponding speed or torque at the electric motor.

[0070] The second means for determining the delivery height and flow rate can in principle be set up to carry out any procedure for determining the operating point.

[0071] In one embodiment, the second means can include an evaluation and processing unit for acquiring and processing the measurement signals from sensors for measuring pressure or differential pressure and / or volumetric flow rate. For this purpose, the evaluation and processing unit can, for example, include an amplifier, an analog-to-digital converter, a working memory, a filter, and / or a processor for signal processing, and optionally a protocol-based communication interface if one of the sensors provides measurement data via a communication protocol. In the embodiment for determining the delivery head and flow rate by measurement, the centrifugal pump unit also includes corresponding sensors for measuring the pressure or differential pressure and / or the flow rate.These sensors can be structurally integrated into the centrifugal pump unit, or be independent of it and connected to the pump electronics, more precisely to the communication interface, via a suitable communication link, wired (cable) or wireless (e.g. Bluetooth, WLAN, ZigBee, RFID).

[0072] As an alternative to the aforementioned design variant, instead of a sensor for determining the volume flow rate, the electrical power consumption can be determined and the volume flow rate calculated from this, for example by applying the affinity laws or by comparing the current power consumption P with a previously determined table of power values ​​or by calculation based on a power curve P(Q,n), which may have been previously determined and stored as a formula in a memory of the second means.

[0073] In another embodiment, the second means for determining the delivery head and flow rate can also act on the speed control or torque control and provide it with a further excitation signal FA(t), which changes with a second excitation frequency fA higher than the first excitation frequency fg and is superimposed on the setpoint N0 for the current operating point. The second means then further comprise an evaluation unit configured to determine the flow rate from the system response to the excitation with the second frequency, as described in European patent application EP 3123033 A1. The evaluation unit is then also configured to calculate the delivery head from the flow rate.

[0074] In another embodiment, the second means for determining the delivery head and flow rate can include a control-engineering observer with a mathematical model of the centrifugal pump unit and the connected hydraulic system, and be configured to determine the delivery head and flow rate from this model, as described in the Luxembourg application LU501040 dated 17.12.2021.

[0075] The third means for determining the amplitudes of the delivery head and delivery flow fluctuations include, in particular, an integration unit. It is configured, on the one hand, to form the product of the determined delivery flow Q and a sinusoidal signal with the excitation frequency f A and to integrate over at least one period of the excitation signal FA (t), and, on the other hand, to form the product of the determined delivery head H and a sinusoidal signal with the excitation frequency f A and to integrate over at least one period of the excitation signal FA (t) in order to determine the amplitudes Q 1 , H 1.

[0076] The fourth means for determining the current operating point of the centrifugal pump unit are designed to determine the DC components Q₀ and H₀ of the delivery head fluctuation ΔH and the delivery flow fluctuation ΔQ, and include a second integration unit for this purpose. They are designed, on the one hand, to integrate the determined delivery flow Q over at least one period of the excitation signal FA(t), and on the other hand, to integrate the determined delivery head H over at least one period of the excitation signal FA(t) in order to determine the DC components Q₀ and H₀.

[0077] The fifth means for determining the current hydraulic resistance Rh comprise a first calculation unit in which equation Eq. 17 is implemented. It is designed to insert the calculated values ​​of the amplitudes H1, Q1 and the value of the DC component Q0 of the flow rate into this equation and to evaluate the equation in order to determine or estimate the hydraulic resistance Rh.

[0078] The sixth method for determining the static head Hstatic comprises a second calculation unit in which equation 18 or 19 is implemented. It is designed to insert the calculated values ​​of the DC components H0, Q0, and the hydraulic resistance Rh, and, in the case of using equation 18, also the value of the amplitude Q1 of the flow rate fluctuation, into the corresponding equation 18 or 19 and to evaluate this equation in order to determine or estimate the static head Hstatic.

[0079] The method according to the invention can be activated or executed at any time during the operation of the centrifugal pump unit in order to determine the static delivery head H static, for example by manual activation by an installer or maintenance technician or by the pump itself.

[0080] The process can also be permanently active during operation. The current operating point does not need to be abandoned in either case, so the process is barely noticeable externally and does not affect the operation of other system components.

[0081] It should be noted that the foregoing description is given merely as an example for illustrative purposes and in no way limits the scope of protection of the invention. Features of the invention that are indicated as "may", "exemplary", "preferred", "optional", "ideal", "advantageous", "if applicable", "suitable" or the like are to be considered purely optional and likewise do not limit the scope of protection, which is exclusively defined by the claims.

Claims

1. Method for determining the static pumping head (Hstatic) of a speed-controlled centrifugal pump assembly operated in a working point (B) in an open hydraulic system, characterised by the pumping head (H) of the centrifugal pump assembly in the working point (B) being modulated to obtain a pumping head fluctuation (ΔH) with an excitation frequency (fg) that is so low that a flow rate fluctuation (ΔQ) is caused, in which the pumping head fluctuation (ΔH) and the flow rate fluctuation (ΔQ) are used to determine modulation parameters (H0, Q0, H1, Q1) that are used to determine the static pumping head (Hstatic).

2. Method according to claim 1, characterised by the modulation of the pumping head (H) being effected by applying a setpoint value for the existing operating speed (N0) in the working point (B) or the existing operating torque in the working point (B) with a periodic excitation signal (Fg(t)) of an excitation frequency (fg).

3. Method according to claim 1 or 2, characterised by the excitation frequency (fg) being less than 1 Hz, preferably between 0.5 Hz and 0.05 Hz, notably approx. 0.1 Hz.

4. Method according to one of the preceding claims, characterised by the static pumping head (Hstatic) being determined using an equation describing the system curve (1) of the hydraulic system, which specifies the pumping head (H) required for a certain flow rate (Q) and comprises a quadratic term, the coefficient of which specifies the hydraulic resistance (R) of the system.

5. Method according to claim 4, characterised by the equation only comprising the quadratic term and a flow rate independent term that specifies the static pumping head (Hstatic).

6. Method according to one of the preceding claims, characterised by the modulation parameters (H0, Q0, H1, Q1) being the direct component (H0, Q0) and the amplitude (H1, Q1) of the pumping head (H) and the flow rate (Q).

7. Method according to claim 6, characterised by the direct component (H0) of the pumping head (H) being determined by integration of the pumping head (H) over at least one period and / or the direct component (Q0) of the flow rate (Q) being determined by integration of the flow rate (Q) over at least one period.

8. Method at least according to claim 6 or 7, characterised by the amplitude (H1) of the pumping head fluctuation (ΔH) being determined by integration of the product of the pumping head (H) and a sine or cosine signal with the excitation frequency (fg) over at least one period and / or the amplitude (Q1) of the flow rate fluctuation (ΔQ) being determined by integration of the product of the flow rate (H) and a sine or cosine signal with the excitation frequency (fg) over at least one period.

9. Method at least according to claim 4 and 6, characterised by the hydraulic resistance (R) of the system in the working point (B) being determined using the amplitude (H1, Q1) of the pumping head fluctuation (ΔH) and the flow rate fluctuation (ΔQ) and the direct component (Q0) of the flow rate (Q).

10. Method at least according to claim 4 and 6, characterised by the hydraulic resistance (R) of the system being determined using the equation R = H 1 Q 1 ⋅ 2 Q 0 , where R is the hydraulic resistance, H1 is the amplitude of the pumping head fluctuation (ΔH), Q1 is the amplitude of the flow rate fluctuation (ΔQ) and Q0 is the direct component of the flow rate (Q).

11. Method according to one of the claims 6 through 8 and one of the claims 9 or 10, characterised by the static pumping head (Hstatic) being determined using the direct components (H0, Q0) of the pumping head (H) and the flow rate (Q)and the hydraulic resistance of the system according to the equation Hstatic = H0 - R · Q02, where Hstatic is the static pumping head, H0 is the direct component of the pumping head (H), Q0 is the direct component of the flow rate (Q) and R is the hydraulic resistance of the system.

12. Speed-controllable centrifugal pump assembly comprising a centrifugal pump, an electric motor driving the same and pump electronics for the closed-loop and / or open-loop control of the electric motor, characterised by the pump electronics being configured to execute one of the claims 1 through 10.