JP7460480B2 - Three-phase heater phase current detection device and method - Google Patents

Description

The present invention relates to a three-phase heater phase current detection technology for calculating the phase currents flowing through a delta-connected three-phase heater.

The lifespan of the three resistors constituting the three-phase heater is determined based on the comparison result between the initial resistance value and the actually measured resistance value. Therefore, in diagnosing the lifespan of a three-phase heater, it is extremely effective to measure the resistance value of each resistor. However, in many three-phase heaters, each resistor is integrated, so it is difficult to directly detect the voltage and current applied to these resistors individually. For example, in the case of delta connection, it is difficult to directly detect the phase current, and in the case of star connection, it is difficult to directly detect the phase voltage.
Conventionally, a technique has been proposed for estimating phase current when detecting the resistance value of each resistor in such a three-phase heater (see, for example, Patent Document 1).

JP 2016-110732 A

In the prior art described above, when the angle between the phases of a three-phase power supply is known, the estimated value of the phase current is updated by performing feedback processing on the estimated value of the phase current. Therefore, when estimating the phase current, it is necessary to perform feedback processing, that is, repeated calculations. However, depending on the type of three-phase heater, the change in resistance value with respect to ambient temperature may be large. For this reason, the method of performing repeated calculations has a problem in that tracking of the estimated value becomes slow due to changes in the resistance value.

The present invention is intended to solve these problems, and aims to provide a three-phase heater phase current detection technology that can calculate the phase current flowing through a delta-connected three-phase heater without the need for repeated calculations.

In order to achieve such an object, the three-phase heater phase current detection device according to the present invention applies voltage to a three-phase heater having three resistors connected in delta through three power supply lines. a detection circuit configured to detect a line current detected by the detection circuit; and an arithmetic processing configured to calculate a phase current flowing through each of the three resistors based on the line current detected by the detection circuit. and an effective value calculation unit configured to calculate an effective value of the line current, and an angle between the line current and the phase current based on the effective value of the line current. and a phase current calculation section configured to calculate the effective value of the phase current based on the effective value of the line current and the angle. .

Further, in one configuration example of the three-phase heater phase current detection device according to the present invention, the angle calculation unit calculates three interior angles of a triangle whose three sides are the effective values of the line current, and The angle between the line current and the phase current is calculated based on the internal angle.

Further, in one configuration example of the three-phase heater phase current detection device according to the present invention, the angle calculation unit calculates the line current Ir and the line current among the three line currents Ir, Is, It that constitute the line current. Is, the line current Ir and the line current It, the internal angles formed by the line current Is and the line current It are angles ∠O, ∠P, ∠Q, and the angle between the phase current Irs and the line current Is is α, The angle between the phase current Itr and the line current Ir is β, the angle between the phase current Ist and the line current It is γ, and the numerator and denominator of the fraction representing the value of tan(α) are variables X and Y. In this case, the variables X and Y and angles α, β, and γ are calculated using equation (1) described later.

Further, in one configuration example of the three-phase heater phase current detection device according to the present invention, the phase current calculation unit calculates the line current Ir and the line current among the three line currents Ir, Is, It that constitute the line current. The angle between the phase current Irs of the current Is and the line current Is is α, the angle between the line current Ir and the phase current Itr of the line current It, and the line current Ir is β, and the phase of the line current Is and the line current It is When the angle formed by the current Ist and the line current It is γ, the phase currents Irs, Itr, and Ist are calculated by solving the simultaneous equations of Equation (2) described later.

Further, another three-phase heater phase current detection device according to the present invention detects line currents applied to a three-phase heater having three resistors connected in delta via three power supply lines. and an arithmetic processing circuit configured to calculate a phase current flowing through each of the three resistors based on the line current detected by the detection circuit, The arithmetic processing circuit includes an effective value calculation unit configured to calculate the effective value of the line current, and an intersection point where the phase current intersects three vertices of a triangle whose three sides are the effective value of the line current. and a position calculation unit configured to calculate the coordinate position of the phase current, and a position calculation unit configured to calculate the effective value of the phase current based on the distance between the apex and the intersection point determined from the coordinate positions of the apex and the intersection point. and a phase current calculation section.

Further, in one configuration example of the three-phase heater phase current detection device according to the present invention, the position calculation unit determines that at least two of the three sides are chords and that the circumferential angle of the chord is The configuration is such that each arc whose angle is 120° is determined, and the point where these arcs intersect is specified as the intersection point.

The three-phase heater phase current detection method according to the present invention is a three-phase heater phase current detection method used in a three-phase heater phase current detection device that includes a detection circuit configured to detect line currents applied to a three-phase heater having three delta-connected resistors via three power supply lines, and a calculation processing circuit configured to calculate the phase currents flowing through each of the three resistors based on the line currents detected by the detection circuit, and includes an effective value calculation step in which the calculation processing circuit calculates the effective value of the line current, an angle calculation step in which the calculation processing circuit calculates the angle between the line current and the phase current based on the effective value of the line current, and a phase current calculation step in which the calculation processing circuit calculates the effective value of the phase current based on the effective value of the line current and the angle.

Further, another three-phase heater phase current detection method according to the present invention detects line currents applied to a three-phase heater having three resistors connected in a delta connection through three power supply lines. and an arithmetic processing circuit configured to calculate a phase current flowing through each of the three resistors based on the line current detected by the detection circuit. A three-phase heater phase current detection method used in a heater phase current detection device, comprising: an effective value calculation step in which the arithmetic processing circuit is configured to calculate an effective value of the line current; and the arithmetic processing circuit. a coordinate calculating step configured to calculate coordinate positions of an intersection point where the phase current intersects three vertices of a triangle whose three sides are the effective values of the line current; and the arithmetic processing circuit. and a phase current calculation step configured to calculate an effective value of the phase current based on a distance between the apex and the intersection point determined from the coordinate position.

According to the present invention, it is possible to calculate the phase current flowing in a delta-connected three-phase heater without requiring repeated calculations for phase current estimation as in the prior art.

FIG. 1 is a block diagram showing a configuration of a three-phase heater current detection device according to a first embodiment. FIG. 2 is a flowchart showing phase current detection processing according to the first embodiment. FIG. 3 is an explanatory diagram showing the angle derivation process. FIG. 4 is an explanatory diagram showing the phase current derivation process. FIG. 5 is a block diagram showing a configuration of a three-phase heater current detection device according to the second embodiment. FIG. 6 is a flowchart showing a phase current detection process according to the second embodiment. FIG. 7 is an explanatory diagram showing a circular arc Ar whose chord is the side OP. FIG. 8 is an explanatory diagram showing a circular arc As having a chord at side OQ. FIG. 9 is an explanatory diagram showing an arc At whose chord is the side PQ. FIG. 10 is an explanatory diagram showing the phase current derivation process.

Next, an embodiment of the present invention will be described with reference to the drawings.
[First embodiment]
First, a three-phase heater phase current detection device 10 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of the three-phase heater phase current detection device according to the first embodiment.

[Three-phase heater phase current detection device]
The three-phase heater phase current detection device 10 is used in a factory or a plant, and detects a three-phase heater connected thereunder according to an instruction from a host device 30 such as an industrial controller connected via a communication line NW. This is a device that individually detects the phase currents Irs, Itr, and Ist flowing through the three resistors R1, R2, and R3 that make up the resistor 20. The three-phase heater phase current detection device 10 may be an independent device; for example, the three-phase heater phase current detection device 10 may be a three-phase power regulator that adjusts the power supplied to the three-phase heater 20. Some or all of the three-phase heater phase current sensing device 10 may be implemented in separate equipment.

[Three-phase heater]
The three-phase heater 20 is composed of three resistors (heaters) R1, R2, and R3, and converts three-phase AC power sources R, S, and T supplied via three power feed lines Lr, Ls, and Lt into thermal energy and outputs the thermal energy. In this embodiment, as shown in FIG. 1, a case will be described as an example in which the resistors R1, R2, and R3 are delta-connected.

That is, in the three-phase heater 20, one end of the resistor R1 is connected to the node N1 to which the R phase (first phase) of the three-phase AC power supply is supplied via the power supply line Lr, and the other end of the resistor R1 is The end is connected to a node N2 to which the S phase (second phase) of the three-phase AC power supply is supplied via the power supply line Ls. Further, one end of resistor R2 is connected to node N2, and the other end of resistor R2 is connected to node N3, which is supplied with T phase (third phase) of the three-phase AC power supply via power supply line Lt. has been done. Further, one end of the resistor R3 is connected to the node N3, and the other end of the resistor R3 is connected to the node N1.

[Configuration of three-phase heater current detection device]
Next, with reference to FIG. 1, a configuration of the three-phase heater phase current detection device 10 according to the present embodiment will be described in detail.
As shown in FIG. 1, the three-phase heater phase current detection device 10 mainly includes a communication I/F 11, an operation input circuit 12, a display circuit 13, a detection circuit 14, a memory circuit 15, and an arithmetic processing circuit 16.

[Communication I/F]
The communication I/F 11 is configured to perform data communication with the host device 30 via the communication line NW.
[Operation input circuit]
The operation input circuit 12 includes operation input devices such as operation keys, operation switches, and a touch panel, and is configured to detect an operator's operation and output it to the arithmetic processing circuit 16 .
[Display circuit]
The display circuit 13 is composed of a display device such as an LED or an LCD, and is configured to display various information output from the arithmetic processing circuit 16.

[Detection circuit]
The detection circuit 14 is configured to detect currents flowing through each of the power supply lines Lr, Ls, and Lt and output them to the arithmetic processing circuit 16. In this embodiment, the detection circuit 14 is configured to detect line currents (instantaneous values) flowing through the power supply lines Lr _, Ls, and Lt.

[Memory circuit]
The memory circuit 15 is made up of a memory circuit such as a semiconductor memory, and is configured to store various processing data and a program 15P used in the resistance value calculation process executed by the arithmetic processing circuit 16.
The program 15P is a program for implementing various processing sections used in the resistance value calculation process by being executed by the CPU of the arithmetic processing circuit 16. This program 15P is read out from an external device or a recording medium (neither of which are shown) connected to the three-phase heater phase current detection device 10, and is stored in advance in the memory circuit 15.

The arithmetic processing circuit 16 is configured to calculate the phase currents Irs, Itr, and _Ist flowing through the three resistors R1, R2, and R3 of the three-phase heater, respectively, based on the line currents _Ir , _Is , and It detected by the detection circuit 14. The arithmetic processing circuit 16 has a CPU and its peripheral circuits, and has a function of realizing various processing units used for the phase current calculation process by making the hardware and software work together by reading out a program 15P from the memory circuit 15 and executing it on the CPU.
The main processing units realized by the arithmetic processing circuit 16 include an effective value calculation unit 16A, an angle calculation unit 16B, and a phase current calculation unit 16C.

[Effective value calculation section]
The effective value calculation unit 16A is configured to calculate the effective values Ir, Is, and It of the line currents based on the instantaneous values of the line currents detected by the detection circuit 14. Below, the effective values Ir, Is, It of the line current may be simply referred to as the line current Ir, Is, It. Further, the effective values Irs, Itr, and Ist of the phase currents are sometimes simply referred to as line currents Irs, Itr, and Ist.

[Angle calculation section]
The angle calculation unit 16B is configured to calculate the angle between the line current and the phase current based on the effective values Ir, Is, and It of the line current calculated by the effective value calculation unit 16A. At this time, the angle calculation unit 16B calculates the three interior angles ∠O, ∠P, and ∠Q of the triangle OPQ whose three sides are the effective values Ir, Is, and It of the line current, and calculates the obtained interior angle ∠O. , ∠P, ∠Q, the angles α, β, and γ between the line current and the phase current are calculated.

Specifically, the angle calculation unit 16B calculates the line current Ir and the line current Is, the line current Ir and the line current It, and the line current Is and the line current among the three line currents Ir, Is, and It that constitute the line current. The interior angles It makes are angles ∠O, ∠P, ∠Q, the angle between phase current Irs and line current Is is α, the angle between phase current Itr and line current Ir is β, and phase If the angle between the current Ist and the line current It is γ, and the numerator and denominator of the fraction representing the value of tan(α) are X, Y, then these X, Y, α, It may be configured to calculate β and γ. The details of equation (1) will be described later.

[Phase current calculation section]
The phase current calculation unit 16C calculates the effective value of the phase current based on the effective values Ir, Is, It of the line current calculated by the effective value calculation unit 16A and the angles α, β, γ calculated by the angle calculation unit 16B. Irs, Itr, Ist are calculated, and the obtained effective values Irs, Itr, Ist of the phase currents are stored in the memory circuit 15 and displayed on the display circuit 13, or sent from the communication I/F 11 to the upper layer via the communication line NW. The information is configured to be distributed to the device 30.

Specifically, among the three line currents Ir, Is, and It that constitute the line current, if the angle between the phase current Irs of the line current Ir and the line current Is and the line current Is is α, the angle between the phase current Itr of the line current Ir and the line current It and the line current Ir is β, and the angle between the phase current Ist of the line current Is and the line current It and the line current It is γ, the phase currents Irs, Itr, and Ist may be calculated by solving the simultaneous equations of the following formula (2). Details of formula (2) will be described later.

[Operation of the first embodiment]
Next, with reference to FIG. 2, the operation of the three-phase heater phase current detection device 10 according to this embodiment will be described. FIG. 2 is a flowchart showing phase current detection processing according to the first embodiment.
When detecting the phase current of the three-phase heater 20, the arithmetic processing circuit 16 of the three-phase heater phase current detection device 10 executes the phase current detection process of FIG. 2.

First, the arithmetic processing circuit 16 uses the effective value calculation unit 16A to calculate the effective values Ir, Is of the line currents, based on the instantaneous values of the line currents flowing through the feeder lines Lr, Ls, Lt, detected by the detection circuit 14. , It is calculated (step S100).
Next, the arithmetic processing circuit 16 uses the angle calculation unit 16B to calculate the angle of the triangle OPQ whose three side lengths are the effective values Ir, Is, It of the line current based on the effective values Ir, Is, It of the line current. The interior angles ∠O, ∠P, and ∠Q are calculated (step S101). The interior angles of a triangle can be found from the lengths of the three sides using the law of cosines.

Subsequently, the arithmetic processing circuit 16 calculates the angles α, β, and γ of the line current and phase current from the internal angles ∠O, ∠P, and ∠Q using the above-mentioned equation (1) using the angle calculation unit 16B. (Step S102).
Thereafter, the arithmetic processing circuit 16 uses the phase current calculation unit 16C to calculate the effective values Ir, Is, It of the line current calculated by the effective value calculation unit 16A, and the angles α, β, γ calculated by the angle calculation unit 16B. Based on the equation (2) described above, the effective values Irs, Itr, and Ist of the phase currents are calculated (step S103), and the series of phase current detection processing is ended.

[Angle derivation process]
Next, the process of deriving the angles α, β, and γ between the line current and the phase current using the above-mentioned equation (1) will be described in detail with reference to Fig. 3. Fig. 3 is an explanatory diagram showing the angle deriving process.
Consider a triangle OPQ with the lengths of the three sides being the effective values Irs, Itr, and Ist of the phase currents, as shown in Fig. 3. As shown in Fig. 1, the phase current Irs is a phase current that occurs between the line current Ir and the line current Is and flows through the resistor R1. The phase current Itr is a phase current that occurs between the line current It and the line current Ir and flows through the resistor R3. The phase current Ist is a phase current that occurs between the line current Is and the line current It and flows through the resistor R2.

When three straight lines passing through vertices O, P, and Q of triangle OPQ intersect at 120° with each other at intersection K within triangle OPQ, the lengths of the line segments KO, KP, and KQ connecting intersection K with vertices O, P, and Q respectively correspond to the magnitudes of the phase currents Irs, Itr, and Ist. This is because in a delta-connected three-phase heater, the difference between two phase current vectors corresponds to the line current vector, and the angle between the phase currents is 120°. Therefore, if the positional relationship between vertices O, P, and Q and intersection K is identified based on the effective values Irs, Itr, and Ist of the phase currents, the phase currents Irs, Itr, and Ist can be found from the lengths of the line segments KO, KP, and KQ.

[Relationship between angles ∠O, ∠P, ∠Q and angles α, β, γ]
First, assuming that the angles of vertices O, P, and Q are ∠O, ∠P, and ∠Q, these angles ∠O, ∠P, and ∠Q can be found from the cosine theorem shown in equation (3) based on the effective values Irs, Itr, and Ist of the phase currents.

Next, as shown in FIG. 3 , if the angle between phase current Irs and line current Is is α, the angle between phase current Itr and line current Ir is β, and the angle between phase current Ist and line current It is γ, the relationship between angles ∠O, ∠P, ∠Q and angles α, β, γ is expressed by the following equation (4).

[How to find the angle]
In this way, if any one of angles α, β, and γ is found, the remaining angles can be found based on equation (4). In the following, as an example, angle α is found first, and angles β and γ are found from angle α. Note that angle β or angle γ may be found first.
Furthermore, in this embodiment, focusing on the fact that the tangent tan(α) of angle α can be expressed as the ratio of sine sin(α) to cosine cos(α), the ratio of sin(α) to cos(α) is defined as X/Y, and after this ratio X/Y is calculated, the angle α is calculated based on the inverse tangent tan ⁻¹ (X/Y) of the ratio X/Y, as shown in the following equation (5).

[Cheba's theorem]
Line segments KO, KP, and KQ shown in FIG. 3 pass through vertices O, P, and Q of triangle OPQ, and intersect at an intersection K in triangle OPQ that is not on a side or its extension. The conditions for establishing such a positional relationship are defined by Ceva's theorem. The following equation (6) is obtained by applying angles α, β, and γ to the inverse trigonometric expression of Ceva's theorem.

[Transformation of the left side]
Next, the left side of equation (6) is transformed. The product-sum formula for trigonometric functions is given by the following equation (7). Therefore, the left side of equation (6) is transformed into the following equation (8).

Now, by introducing the variables w, x, y, and z shown in equation (9) and replacing the addition and subtraction formulas for angles α, β, and γ in equation (8) with the variables w, x, y, and z, the left side of equation (6) is transformed into the following equation (10).

[Transformation of the right side]
Next, the right side of equation (6) is transformed. In the same manner as the left side of equation (6), the right side of equation (6) is transformed using the product-sum formula of trigonometric functions shown in equation (7). Next, the addition and subtraction formulas for angles α, β, and γ are replaced with variables w, x, y, and z. As a result, the right side of equation (6) is transformed into the following equation (11).

Here, the addition theorem of trigonometric functions includes the following equation (12). Therefore, each term on the left side of equation (11) is transformed as shown in equation (13) below.

[Organization of both left and right sides]
Therefore, based on the formula (13) applied to formula (11) and the right-hand side of formula (6) transformed, and the formula (10) obtained by transforming the left-hand side of formula (6), By rearranging both the left and right sides of equation (6), the following equation (14) is obtained.

[Angle derivation]
The variables w, x, y, and z in equation (9) are expressed by angle α and angles ∠O, ∠P, and ∠Q according to equation (4), as shown in the following equation (15).

When each term of equation (14) is calculated based on equation (15), the following equation (16) is obtained. As a result, when formula (16) is applied to formula (14), the following formula (17) is obtained.

Therefore, by transforming this equation (17), the ratio X/Y of sin(α) and cos(α) can be found using equation (18), and based on equation (5), the angle α can be calculated using the following equation ( 19).

In this case, the numerator and denominator of equation (16) correspond to the variables X and Y in equation (5). Furthermore, angles β and γ can be found from angle α based on equation (4). Therefore, variables X and Y can be found from angles ∠O, ∠P, and ∠Q, angle α can be found from the ratio X/Y, and angles β and γ can be found from angle α, resulting in equation (1) described above.

[Phase current derivation process]
Next, with reference to FIG. 4, the process of deriving the phase currents Irs, Itr, and Ist using the above-mentioned equation (2) will be described in detail. FIG. 4 is an explanatory diagram showing the phase current derivation process.
As shown in FIG. 4, the points D, E, and F are where perpendicular lines drawn from the intersection K identified in FIG. 3 to the sides OP, OQ, and PQ intersect the sides OP, OQ, and PQ. Thereby, the line current Ir is divided into two at point D, and is represented by the sum of the current IrO corresponding to the line segment OD and the current IrP corresponding to the line segment PD. Further, the line current Is is divided into two at point E, and is represented by the sum of a current IsO corresponding to the line segment OE and a current IsQ corresponding to the line segment QE. Further, the line current It is divided into two at point F, and is represented by the sum of a current ItP corresponding to the line segment PF and a current ItQ corresponding to the line segment QE.

On the other hand, current IrO is expressed as the product of phase current Irs and cos(60°-β), and current IrP is expressed as the product of phase current Itr and cos(β). Current IsO is expressed as the product of phase current Irs and cos(α), and current IsQ is expressed as the product of phase current Ist and cos(60°-α). Current Itp is expressed as the product of phase current Itr and cos(γ), and current ItQ is expressed as the product of phase current Ist and cos(60°-γ).
Therefore, the line currents Ir, Is, It can be obtained from the phase currents Irs, Itr, Ist and the angles α, β, γ as shown in the above-mentioned equation (2). Therefore, when the line currents Ir, Is, It and the angles α, β, γ are known, equation (2) becomes a simultaneous equation, and by solving this, the phase currents Irs, Itr, Ist can be obtained.

[Advantages of the First Embodiment]
As described above, in this embodiment, the arithmetic processing circuit 16 of the three-phase heater phase current detection device 10 is configured to calculate the effective value of the line current detected by the detection circuit 14 using the effective value calculation unit 16A, calculate the angle between the line current and the phase current based on the effective value of the line current using the angle calculation unit 16B, and calculate the effective value of the phase current based on the effective value and angle of the line current using the phase current calculation unit 16C.
More specifically, the angle calculation unit 16B is configured to calculate the three interior angles of a triangle whose three sides are the effective values of the line current, and to calculate the angles between the line current and the phase current based on the obtained interior angles.

This makes it possible to calculate the effective value of the line current, the angle between the line current and the phase current, and the effective value of the phase current using preset formulas. Therefore, it is possible to calculate the phase current flowing through a delta-connected three-phase heater without the need for repeated calculations to estimate the phase current as in conventional technology. For this reason, even if the resistance value changes significantly with respect to the ambient temperature depending on the type of three-phase heater, there is no delay in the calculation processing time for the phase current, and the effective value of the phase current can be detected with high accuracy.

In addition, in this embodiment, the angle calculation unit 16B may be configured to calculate X, Y, α, β, and γ according to the above-mentioned formula (1) when the interior angles formed by the line current Ir and the line current Is, the line current Ir and the line current It, and the line current Is and the line current It of the three line currents Ir, Is, and It that constitute the line current are respectively defined as angles ∠O, ∠P, and ∠Q, the angle formed by the phase current Irs and the line current Is is defined as α, the angle formed by the phase current Itr and the line current Ir is defined as β, the angle formed by the phase current Ist and the line current It is defined as γ, and the numerator and denominator of the fraction indicating the value of tan(α) are defined as X and Y.
This makes it possible to instantly obtain angles α, β, and γ by simply applying angles ∠O, ∠P, and ∠Q to equation (1).

In the present embodiment, the phase current calculation unit 16C calculates the relationship between the phase current Irs and the line current Is of the line current Ir and the line current Is among the three line currents Ir, Is, and It that constitute the line current. Let the angle be α, the angle between the line current Itr of the line current Ir and the line current It, and the line current Ir be β, and the angle between the line current Ist and the line current It of the line current Is and the line current It be γ. In this case, the phase currents Irs, Itr, and Ist may be calculated by solving the simultaneous equations of Equation (2) described above.
Thereby, by simply applying the line currents Ir, Is, It and the angles α, β, γ to equation (2), it becomes possible to immediately obtain the phase currents Irs, Itr, Ist.

[Second embodiment]
Next, referring to FIG. 5, a three-phase heater phase current detection device 10 according to a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing the configuration of a three-phase heater phase current detection device according to the second embodiment.
In the first embodiment, an example has been described in which the phase currents Irs, Itr, and Ist are detected from the line currents Ir, Is, and It using trigonometric functions. In this embodiment, a case where phase currents Irs, Itr, and Ist are detected from line currents Ir, Is, and It using coordinate positions will be described as an example. Note that in this embodiment, only a part of the processing unit of the arithmetic processing circuit 16 is different, and other configurations are the same or the same as in the first embodiment. A code is attached.

[Three-phase heater current detection device]
The three-phase heater phase current detection device 10 is used in a factory or a plant, and detects the phase currents Irs, Itr, and Ist flowing through three resistors R1, R2, and R3 constituting a three-phase heater 20 connected thereto, individually, in response to an instruction from a higher-level device 30, such as an industrial controller connected via a communication line NW. The three-phase heater phase current detection device 10 may be an independent device, and part or all of the three-phase heater phase current detection device 10 may be mounted in a device separate from the three-phase heater phase current detection device 10, such as a three-phase power regulator that adjusts the power supplied to the three-phase heater 20.

[Three-phase heater]
The three-phase heater 20 is composed of three resistors (heaters) R1, R2, and R3, and converts three-phase AC power sources R, S, and T supplied via three power feed lines Lr, Ls, and Lt into thermal energy and outputs the thermal energy. In this embodiment, as shown in Fig. 5, a case will be described as an example in which the resistors R1, R2, and R3 are delta-connected.

That is, in the three-phase heater 20, one end of the resistor R1 is connected to the node N1 to which the R phase (first phase) of the three-phase AC power supply is supplied via the power supply line Lr, and the other end of the resistor R1 is The end is connected to a node N2 to which the S phase (second phase) of the three-phase AC power supply is supplied via the power supply line Ls. Further, one end of resistor R2 is connected to node N2, and the other end of resistor R2 is connected to node N3, which is supplied with T phase (third phase) of the three-phase AC power supply via power supply line Lt. has been done. Further, one end of the resistor R3 is connected to the node N3, and the other end of the resistor R3 is connected to the node N1.

[Configuration of three-phase heater current detection device]
Next, the configuration of the three-phase heater phase current detection device 10 according to this embodiment will be described in detail with reference to FIG.
As shown in FIG. 5, the three-phase heater phase current detection device 10 mainly includes a communication I/F 11, an operation input circuit 12, a display circuit 13, a detection circuit 14, a memory circuit 15, and an arithmetic processing circuit 16.

[Communication I/F]
The communication I/F 11 is configured to perform data communication with the higher-level device 30 via the communication line NW.
[Operation input circuit]
The operation input circuit 12 is made up of operation input devices such as operation keys, operation switches, and a touch panel, and is configured to detect operations by an operator and output the operations to the arithmetic processing circuit 16 .
[Display circuit]
The display circuit 13 is made up of a display device such as an LED or an LCD, and is configured to display various information output from the arithmetic processing circuit 16 .

[Detection circuit]
The detection circuit 14 is configured to detect currents flowing through each of the power supply lines Lr, Ls, and Lt and output them to the arithmetic processing circuit 16. In this embodiment, the detection circuit 14 is configured to detect line currents (instantaneous values) flowing through the power supply lines Lr _, Ls, and Lt.

[Memory circuit]
The storage circuit 15 is composed of a storage circuit such as a semiconductor memory, and is configured to store various processing data and a program 15P used in the resistance value calculation process executed by the arithmetic processing circuit 16.
The program 15P is a program that is executed by the CPU of the arithmetic processing circuit 16 to implement various processing units used for resistance value calculation processing. This program 15P is read from an external device or a recording medium (both not shown) connected to the three-phase heater phase current detection device 10 and stored in the storage circuit 15 in advance.

The arithmetic processing circuit 16 calculates phase currents Irs, Itr, Ist flowing through the three resistors R1, R2, R3 of the three-phase heater based on the line currents I _r , I _s , _It detected by the detection circuit 14 . is configured to calculate. The arithmetic processing circuit 16 has a CPU and its peripheral circuits, and by reading out a program 15P from the storage circuit 15 and executing it on the CPU, the arithmetic processing circuit 16 cooperates with hardware and software to create various processing units used for phase current calculation processing. It has the function to realize
The main processing units implemented in the arithmetic processing circuit 16 include an effective value calculation unit 16A, a position calculation unit 16D, and a phase current calculation unit 16E.

[Effective value calculation section]
The effective value calculation unit 16A is configured to calculate the effective values Ir, Is, and It of the line currents based on the instantaneous values of the line currents detected by the detection circuit 14. Below, the effective values Ir, Is, It of the line current may be simply referred to as the line current I _r , I _s , _It . Further, the effective values Irs, Itr, and Ist of the phase currents are sometimes simply referred to as line currents Irs, Itr, and Ist.

[Position calculation section]
The position calculation unit 16D calculates the three vertices O, P, and Q of a triangle OPQ whose three sides are the effective values Ir, Is, and It of the line currents calculated by the effective value calculation unit 16A, and the effective values Irs, Itr of the phase currents. , Ist intersect with each other. A rectangular coordinate system on a plane is used to calculate the coordinate position. At this time, in the orthogonal coordinate system, the triangle OPQ whose three side lengths are the effective values Ir, Is, and It of the line current may be placed at an arbitrary position, for example, by placing one of its vertices at the origin.

[Phase current calculation section]
The phase current calculation unit 16E is configured to calculate the distance between each of the vertices O, P, Q and the intersection K from the coordinate positions of the vertices O, P, Q and the intersection K calculated by the position calculation unit 16D, calculate the effective values Irs, Itr, Ist of the phase currents based on the obtained distances, store the obtained effective values Irs, Itr, Ist of the phase currents in the memory circuit 15, display them on the display circuit 13, or distribute them from the communication I/F 11 to the higher-level device 30 via the communication line NW.

[Operation of the second embodiment]
Next, the operation of the three-phase heater phase current detection device 10 according to the present embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing a phase current detection process according to the second embodiment.
When detecting the phase currents of the three-phase heater 20, the arithmetic processing circuit 16 of the three-phase heater phase current detection device 10 executes the phase current detection process of FIG.

First, the arithmetic processing circuit 16 calculates the effective values Ir, Is, and It of the line currents based on the instantaneous values of the line currents flowing through the power supply lines Lr, Ls, and Lt detected by the detection circuit 14 using the effective value calculation unit 16A (step S200).

Next, the arithmetic processing circuit 16 calculates, based on the effective values Ir, Is, It of the line current, the position calculation unit 16D of the triangle OPQ whose three side lengths are the effective values Ir, Is, It of the line current. The coordinate positions of the three vertices O, P, and Q are calculated (step S201). If the coordinate positions of the vertices O, P, and Q are (Xo, Yo), (Xp, Yp), and (Xq, Yq), respectively, then the effective values of the line currents Ir, Is, and It are calculated using the formula for the distance between two points. Based on this, it is expressed by the following equation (20). Note that the triangle OPQ may be placed at any position, such as placing one of its vertices at the origin.

Subsequently, the arithmetic processing circuit 16 uses the position calculation unit 16D to determine that at least two of the three sides OP, OQ, and PQ of the triangle OPQ are set as a chord, and that the circumferential angle of the chord is 120°. The arcs Ar, As, At are calculated (step S202).

Figure 7 is an explanatory diagram showing an arc Ar with side OP as its chord. The arc Ar has a center at point Zr and a chord at side OP, passing through both vertices O and P. In this case, since the circumferential angle is 120°, the angle at which the radius Rr of the arc Ar intersects with side OP is 30°. Therefore, the radius Rr is 1/√3 of the length of side OP, i.e., the effective value Ir of the line current.

Figure 8 is an explanatory diagram showing the arc As with side OQ as its chord. The arc As has its center at point Zs and its chord at side OQ, and passes through both vertices O and Q. In this case, since the inclination angle is 120°, the angle at which the radius Rs of the arc As intersects with side OQ is 30°. Therefore, the radius Rs is the length of side OQ, i.e., 1/√3 of the effective value Is of the line current.

Figure 9 is an explanatory diagram showing the arc At with side PQ as its chord. The arc At has its center at point Zt and its chord at side PQ, and passes through both vertices P and Q. In this case, since the inclination angle is 120°, the angle at which the radius Rt of the arc At intersects with side PQ is 30°. Therefore, the radius Rt is the length of side PQ, i.e., 1/√3 of the effective value It of the line current.

Therefore, if the position coordinates of points Zr, Zs, and Zt are (Xr, Yr), (Xs, Ys), and (Xt, Yt), respectively, the arcs Ar, As, and At are expressed by the following equation (21). be done.

The point at which at least two of the thus obtained arcs Ar, As, and At intersect corresponds to the intersection point K at which the effective values Irs, Itr, and Ist of the phase currents intersect. This is because, in a delta-connected three-phase heater, the difference between two phase current vectors corresponds to the line current vector, and the angle between the phase currents is 120°.
The arithmetic processing circuit 16 solves the simultaneous equations of equation (21) by the position calculation section 16D, and calculates the position coordinates (Xk, Yk) of the intersection point K (step S203).

Thereafter, the arithmetic processing circuit 16 uses the phase current calculation unit 16E to calculate the coordinate positions (Xo, Yo), (Xp, Yp), (Xq, Yq) of the vertices O, P, and Q calculated by the position calculation unit 16D. and the coordinate position (Xk, Yk) of the intersection K, as shown in FIG. The distance to K is calculated as the effective values Irs, Itr, and Ist of the phase currents (step S204), and the series of phase current detection processing ends.

[Effects of the second embodiment]
As described above, in this embodiment, the arithmetic processing circuit 16 of the three-phase heater phase current detection device 10 calculates the effective value of the line current detected by the detection circuit 14 using the effective value calculation section 16A, and the position calculation section 16D calculates the coordinate positions of the three vertices of a triangle whose three sides are the effective values of the line current and the intersection point where the phase current intersects, and the phase current calculation unit 16E calculates the coordinate position of the apex obtained from the coordinate positions of the vertices and the intersection point. The configuration is such that the effective value of the phase current is calculated based on the distance between the intersection points.
More specifically, the position calculation unit 16D calculates, for at least two of the three sides, arcs where the side is a chord and the circumferential angle of the chord is 120°, and these arcs intersect. It is configured to specify points as intersections.

This makes it possible to calculate the effective value of the line current, the position coordinates of the three vertices and intersections of the triangle, and the effective value of the phase current using preset formulas. Therefore, it is possible to calculate the phase current flowing through a delta-connected three-phase heater without the need for repeated calculations to estimate the phase current as in conventional technology. For this reason, even if the resistance value changes significantly with the ambient temperature depending on the type of three-phase heater, there is no delay in the calculation processing time for the phase current, and the effective value of the phase current can be detected with high accuracy.

[Extended embodiments]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, the respective embodiments can be implemented in any combination within a range that does not contradict each other.

Furthermore, in each of the above embodiments, a delta-connected three-phase heater has been described as an example, but the present invention is not limited to this, and can also be applied to a star-connected three-phase heater. In this case, the line voltages of the feeder lines Lr, Ls, and Lt are used instead of the line currents to find the phase voltages generated across each resistor, and the resistance value of each resistor is calculated from these phase voltages and line currents. By calculating and performing delta-star (Δ-Y) conversion, it is possible to estimate the resistance value of each resistor in a star-connected three-phase heater.

10...Three-phase heater phase current detection device, 11...Communication I/F, 12...Operation input circuit, 13...Display circuit, 14...Detection circuit, 15...Memory circuit, 15P...Program, 16...Calculation processing circuit, 16A...Effective value calculation unit, 16B...Angle calculation unit, 16C, 16E...Phase current calculation unit, 16D...Position calculation unit, 20...Three-phase heater, R1, R2, R3...Resistor (heater), Lr, Ls, Lt...Power supply line, Ir, Is, It...Line current (effective value), O, P, Q...Vertex, K...Intersection, ∠O, ∠P, ∠Q...Angle, α, β, γ...Angle, X, Y...Variable, Irs, Itr, Ist...Phase current (effective value).

Claims (8)

a detection circuit configured to detect line currents applied to a three-phase heater having three delta-connected resistors via three power feeders;
and a processing circuit configured to calculate a phase current flowing through each of the three resistors based on the line current detected by the detection circuit;
The arithmetic processing circuit includes:
an effective value calculation unit configured to calculate an effective value of the line current;
an angle calculation unit configured to calculate an angle between the line current and the phase current based on an effective value of the line current;
a phase current calculation unit configured to calculate an effective value of the phase current based on the effective value of the line current and the angle. The three-phase heater phase current detection device according to claim 1,
The angle calculation unit calculates three interior angles of a triangle whose three sides are the effective values of the line current, and calculates the angle between the line current and the phase current based on the obtained interior angles. A three-phase heater phase current detection device comprising: 3. The three-phase heater phase current detection device according to claim 1,
the angle calculation unit is configured to calculate the variables X and Y and the angles α, β, and γ by the following equation, where the interior angles formed by the line current Ir and the line current Is, the line current Ir and the line current It, and the line current Is and the line current It are angles ∠O, ∠P, and ∠Q, respectively, of the three line currents Ir, Is, and It that constitute the line current, the angle formed by the phase current Irs and the line current Is is α, the angle formed by the phase current Itr and the line current Ir is β, and the angle formed by the phase current Ist and the line current It is γ, and the numerator and the denominator of a fraction indicating a value of tan(α) are variables X and Y:

In the three-phase heater phase current detection device according to any one of claims 1 to 3,
The phase current calculation unit calculates the line current Ir by setting the angle between the phase current Irs and the line current Is of the line current Ir and the line current Is to α among the three line currents Ir, Is, and It constituting the line current. When the angle between the phase current Itr of the line current It and the line current Ir is β, and the angle between the line current Is and the phase current Ist of the line current It and the line current It is γ, solve the following simultaneous equations. A three-phase heater phase current detection device, characterized in that it is configured to calculate phase currents Irs, Itr, and Ist.

a detection circuit configured to detect line currents applied to a three-phase heater having three delta-connected resistors via three power supply lines, respectively;
an arithmetic processing circuit configured to calculate a phase current flowing through each of the three resistors based on the line current detected by the detection circuit;
The arithmetic processing circuit is
an effective value calculation unit configured to calculate an effective value of the line current;
a position calculation unit configured to calculate the coordinate position of an intersection point where the phase current intersects three vertices of a triangle whose three sides are the effective value of the line current;
A three-phase heater comprising: a phase current calculation unit configured to calculate an effective value of the phase current based on a distance between the apex and the intersection point determined from the coordinate positions of the apex and the intersection point. Phase current detection device. 6. The three-phase heater phase current detection device according to claim 5.
the position calculation unit is configured to determine, for at least two of the three sides, arcs whose chords are the sides and whose inclination angles are 120°, and to identify, as the intersection points, the points at which these arcs intersect. A three-phase heater phase current detection method for use in a three-phase heater phase current detection device including: a detection circuit configured to detect line currents applied via three power feeders to a three-phase heater having three delta-connected resistors; and an arithmetic processing circuit configured to calculate phase currents flowing through each of the three resistors based on the line currents detected by the detection circuit, the method comprising:
an effective value calculation step, in which the processing circuitry is configured to calculate an effective value of the line current;
an angle calculation step, in which the processing circuitry is configured to calculate an angle between the line current and the phase current based on an effective value of the line current;
and a phase current calculation step, the calculation processing circuit being configured to calculate an effective value of the phase current based on the effective value of the line current and the angle. A three-phase heater phase current detection method for use in a three-phase heater phase current detection device including: a detection circuit configured to detect line currents applied via three power feeders to a three-phase heater having three delta-connected resistors; and an arithmetic processing circuit configured to calculate phase currents flowing through each of the three resistors based on the line currents detected by the detection circuit, the method comprising:
an effective value calculation step, in which the processing circuitry is configured to calculate an effective value of the line current;
a coordinate calculation step in which the arithmetic processing circuit calculates coordinate positions of three vertices of a triangle whose three sides are the effective values of the line currents and the intersection points where the phase currents intersect;
and a phase current calculation step in which the arithmetic processing circuit is configured to calculate an effective value of the phase current based on a distance between the vertex and the intersection obtained from the coordinate position.

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