Adaptive power control method for multi-condition resistance heating device

Abstract

The application discloses a self-adaptive power control method of a multi-working-condition resistance heating device, and relates to the technical field of automatic control.The method comprises the following steps: step one: instantaneous voltage sample value sequences and instantaneous current sample value sequences of three phases are collected by using a high-frequency synchronous sampling array, so as to construct a dynamic impedance topology distortion model of a three-phase unbalanced load; step two: a load distortion guide vector and a total power demand radius are introduced into a vector orthogonal projection intercepting algorithm based on a virtual rotating coordinate system, so as to realize the generation of active and reactive power separation control instructions; and step three: a dynamically optimized asymmetric triggering phase sequence is generated, and active power modulation and reactive power correction are implemented, so that the resistance heating device realizes self-adaptive power control under multi-working conditions.The application can continuously maintain accurate power output and current balance in the process of load change and working condition switching, and significantly improves the response speed, energy efficiency level and grid side operation stability of the resistance heating device.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology, and in particular to an adaptive power control method for multi-condition resistance heating devices, which belongs to the category of industrial control software. Background Technology

[0002] Resistance heating devices are widely used in industrial heating processes. A typical structure consists of a three-phase power supply, a heating load, and a trigger control unit. In most operating conditions, the heating load exhibits significant time-varying characteristics, such as non-linear changes in resistance with increasing temperature, variations in the thermal conductivity of the medium within the heating chamber with varying moisture content, and contact aging at the three-phase equipment connection terminals. These factors make it difficult to maintain balance during operation. Traditional three-phase resistance heating systems typically employ fixed trigger phase sequence, fixed active power regulation algorithms, and simple temperature closed-loop control. While they can maintain relatively stable power output when load characteristics do not change significantly, they often exhibit slow response, unstable power regulation, or significant reactive power fluctuations under conditions of multiple operating condition switching or increased load imbalance.

[0003] In existing technologies, a common approach is to estimate the load condition by detecting the root mean square (RMS) values ​​of three-phase voltage and current, and then adjust the power output of the temperature control circuit based on changes in load impedance. However, this type of estimation is based on periodic averages and cannot reflect transient load changes. Especially when there are sudden changes in the heat absorption rate of the heating medium, aging heating elements, or large power grid fluctuations, the instantaneous changes in the three-phase load often cannot be accurately reflected by the RMS values. This causes the power adjustment commands generated by the control system to lag behind the actual heating demand, and the accumulation of control errors leads to temperature overshoot, insufficient heating, or even frequent start-stop cycles.

[0004] Some existing technologies attempt to regulate power output through phase control, but most implementations treat the three phases as a symmetrical system, adjusting the firing angle only for one or two phases, without considering the impact of impedance differences between the three phases on firing angle distribution. For example, when the load is further increased, the resistance change of one phase may be significantly greater than that of the other two phases, but traditional firing angle adjustment strategies still adjust according to a fixed rule. As a result, the effective voltage area obtained by the phase with high impedance is insufficient, which further differentiates the three-phase currents and worsens the degree of three-phase imbalance. Summary of the Invention

[0005] The purpose of this invention is to provide an adaptive power control method for multi-condition resistance heating devices, which can maintain accurate power output and current balance during load changes and condition switching, significantly improving the response speed, energy efficiency, and grid-side operational stability of resistance heating devices. Overall, it outperforms traditional heating control methods that rely on static models or fixed triggering strategies.

[0006] To address the aforementioned technical problems, this invention provides an adaptive power control method for a multi-condition resistance heating device, the method comprising:

[0007] Step 1: Use a high-frequency synchronous sampling array to collect the instantaneous voltage and current sampling sequences of the three phases, calculate the instantaneous impedance magnitude sequence, and establish three reference phase axes with an angle of 120 degrees between them in a two-dimensional Euclidean plane coordinate system with the origin as the center. Based on the instantaneous impedance magnitude, determine the impedance characteristic endpoints on each reference phase axis and connect them to form a three-phase load impedance distribution triangle. Based on the three-phase load impedance distribution triangle, determine the load distortion guiding vector, and define the difference between the real-time temperature value of the heating cavity and the target process temperature value as the total power demand radius, thereby constructing a dynamic impedance topology distortion model of a three-phase unbalanced load.

[0008] Step 2: Import the load distortion guide vector and total power demand radius into the vector orthogonal projection interception algorithm based on the virtual rotating coordinate system. Use the synchronous rotating dynamic coordinate system to determine the optimal operating balance point of the system through orthogonal projection, generate the active current drive command amplitude and reactive phase compensation command offset, and realize the generation of active and reactive power separation control commands.

[0009] Step 3: The power drive unit executes a dynamic phase sequence optimization modulation strategy on the three-phase thyristor array according to the active current drive command amplitude and reactive phase compensation command bias, and in combination with the geometric characteristics of the three-phase load impedance distribution triangle. This generates a dynamically optimized asymmetric trigger phase sequence and implements active modulation and reactive correction, enabling the resistance heating device to achieve adaptive power control under multiple operating conditions.

[0010] Furthermore, in step one, a high-frequency synchronous sampling array is set at the power input end of the heating device. Within a single operating cycle, the three-phase line is synchronously sampled at a fixed sampling period to obtain the instantaneous voltage sampling value sequence and instantaneous current sampling value sequence of the three phases. Then, a point-by-point division operation is performed on the instantaneous voltage sampling value and instantaneous current sampling value of each phase to generate the corresponding instantaneous impedance modulus value sequence.

[0011] Furthermore, in step one, in the two-dimensional Euclidean coordinate system, three reference phase axes corresponding to phases A, B, and C are established with the origin as the center, and they are at an angle of 120 degrees to each other. On each reference phase axis, the impedance characteristic endpoints are calibrated according to the current value in the instantaneous impedance magnitude sequence of the corresponding phase. The three impedance characteristic endpoints on the three reference phase axes are connected in sequence with straight line segments to form a three-phase load impedance distribution triangle.

[0012] Furthermore, in step one, the geometric centroid of the three-phase load impedance distribution triangle is obtained by calculating the arithmetic mean of the coordinates of the three vertices of the triangle. The line connecting the origin and the geometric centroid is defined as the load distortion guiding vector. The total power demand radius is determined based on the difference between the real-time temperature value of the heating cavity collected by the temperature sensor and the target process temperature value. The load distortion guiding vector and the total power demand radius are used together as parameters of the dynamic impedance topology distortion model of the three-phase unbalanced load.

[0013] Furthermore, in step two, the vector orthogonal projection interception algorithm based on the virtual rotating coordinate system is executed by the embedded central processing unit. The embedded central processing unit uses the angle information synchronized with the fundamental frequency of the power grid to construct a synchronous rotating dynamic coordinate system in the two-dimensional Euclidean plane coordinate system. The vertical axis of the synchronous rotating dynamic coordinate system is defined as the active power reference axis, and the horizontal axis perpendicular to the active power reference axis is defined as the reactive power reference axis.

[0014] Furthermore, in step two, the embedded central processing unit draws an ideal power output circle with the origin of the synchronous rotating dynamic coordinate system as the center and the radius of the total power demand as the radius. The load distortion guide vector is translated into the synchronous rotating dynamic coordinate system to obtain the distortion reference vector. The load characteristic scanning ray is drawn from the origin of the synchronous rotating dynamic coordinate system along the direction of the distortion reference vector. The geometric intersection of the load characteristic scanning ray and the ideal power output circle is determined as the optimal operating balance point of the system.

[0015] Furthermore, in step two, the embedded central processing unit draws perpendicular lines from the system's optimal operating equilibrium point to the active power reference axis and the reactive power reference axis, respectively, to determine the foot of the perpendicular on the active power reference axis and the foot of the perpendicular on the reactive power reference axis. Through geometric measurement, the length of the line segment from the origin of the synchronous rotating dynamic coordinate system to the foot of the perpendicular on the active power reference axis is obtained, and this length is assigned as the active power current drive command amplitude. The length of the line segment from the origin of the synchronous rotating dynamic coordinate system to the foot of the perpendicular on the reactive power reference axis is obtained, and the direction sign is determined according to whether the foot of the perpendicular is located on the positive or negative half-axis of the reactive power reference axis. The length of the line segment with the direction sign from the origin of the synchronous rotating dynamic coordinate system to the foot of the perpendicular on the reactive power reference axis is assigned as the reactive power phase compensation command offset.

[0016] Furthermore, in step three, the dynamic phase sequence optimization modulation strategy includes phase sequence reconfiguration, active power modulation, and reactive power correction. During phase sequence reconfiguration, the power drive unit calculates the three side lengths of the three-phase load impedance distribution triangle, sorts the three side lengths according to their numerical values, selects the two vertices corresponding to the longest side length as the high impedance phase pair, and selects the two vertices corresponding to the shortest side length as the low impedance phase pair. In the subsequent AC grid cycle, the triggering order of the three-phase thyristor array is set according to the order of high impedance phase pair priority and low impedance phase pair follow, forming a dynamically optimized asymmetric triggering phase sequence.

[0017] Furthermore, in the active power modulation process in step three, under the dynamically optimized asymmetric triggering phase sequence, the power drive unit uses pulse width modulation technology to extract the voltage waveform corresponding to the active power drive command amplitude within the conduction range of each phase thyristor according to the active current drive command amplitude, so as to meet the heating power demand reflected by the total power demand radius.

[0018] Furthermore, in the reactive power correction process in step three, the power drive unit superimposes a reactive power phase compensation command bias on the natural zero-crossing trigger time of each phase thyristor. When the reactive power phase compensation command bias is positive, the trigger time of the thyristor is shifted backward along the voltage waveform direction to generate an inductive reactive power cancellation effect. When the reactive power phase compensation command bias is negative, the trigger time of the thyristor is shifted forward along the voltage waveform direction to generate a capacitive reactive power cancellation effect. Thus, while executing the dynamic phase sequence optimization modulation strategy, the reactive power distribution of each phase is improved.

[0019] The adaptive power control method for the multi-condition resistance heating device of the present invention has the following beneficial effects:

[0020] Because this invention uses a high-frequency synchronous sampling method to record the instantaneous impedance characteristics of the three phases in real time and forms a three-phase load impedance distribution triangle in a two-dimensional Euclidean coordinate system, the degree of load imbalance is clearly presented geometrically. This enables accurate identification of the direction and intensity of impedance distortion in each control cycle, providing a reliable basis for subsequent adaptive power allocation.

[0021] By introducing a load distortion guide vector and a total power demand radius, this invention maps temperature control requirements and load imbalance states to the same geometric space, enabling the control system to simultaneously meet thermal and electrical balance requirements. The vector orthogonal projection interception algorithm based on a virtual rotating coordinate system accurately separates active power drive components and reactive power compensation components using only geometric drawing and basic projection relationships, without relying on frequency domain analysis. It boasts advantages such as low computational complexity and high real-time performance, allowing the active current drive command amplitude and reactive power phase compensation command offset to be continuously and smoothly adjusted according to operating conditions.

[0022] In the dynamic phase sequence optimization modulation strategy, this invention utilizes the difference in side lengths of the three-phase load impedance distribution triangle to identify high-impedance phase pairs and low-impedance phase pairs. By dynamically adjusting the triggering sequence and triggering angle, the high-impedance phases obtain a more suitable conduction window under the same power demand, thereby improving current distribution and reducing heat generation, oscillation, and energy loss caused by load imbalance. Furthermore, by combining active power modulation and reactive power correction, the three-phase system exhibits a more stable apparent power characteristic to the power grid, reducing reactive power fluctuations and improving the stability of the heating device during multi-condition switching. Overall, this invention achieves unified closed-loop control of load state identification, power matching, and phase sequence modulation, significantly improving the response speed, energy efficiency, and operational reliability of the resistance heating device. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 A schematic diagram illustrating the geometric construction principle of the three-phase load impedance distribution triangle and load distortion guiding vector provided in an embodiment of the present invention;

[0025] Figure 2 A schematic diagram illustrating the principle of the vector orthogonal projection interception algorithm based on a virtual rotating coordinate system provided in an embodiment of the present invention;

[0026] Figure 3 The time-domain current response waveform of the multi-condition resistance heating device provided in this embodiment of the invention after performing adaptive power control;

[0027] Figure 4 This is a schematic diagram of firing angle modulation under dynamic phase sequence optimization provided in an embodiment of the present invention. Detailed Implementation

[0028] An adaptive power control method for a multi-condition resistance heating device, the method comprising:

[0029] Step 1: Use a high-frequency synchronous sampling array to collect the instantaneous voltage and current sampling sequences of the three phases, calculate the instantaneous impedance magnitude sequence, and establish three reference phase axes with an angle of 120 degrees between them in a two-dimensional Euclidean plane coordinate system with the origin as the center. Based on the instantaneous impedance magnitude, determine the impedance characteristic endpoints on each reference phase axis and connect them to form a three-phase load impedance distribution triangle. Based on the three-phase load impedance distribution triangle, determine the load distortion guiding vector, and define the difference between the real-time temperature value of the heating cavity and the target process temperature value as the total power demand radius, thereby constructing a dynamic impedance topology distortion model of a three-phase unbalanced load.

[0030] Step 2: Import the load distortion guide vector and total power demand radius into the vector orthogonal projection interception algorithm based on the virtual rotating coordinate system. Use the synchronous rotating dynamic coordinate system to determine the optimal operating balance point of the system through orthogonal projection, generate the active current drive command amplitude and reactive phase compensation command offset, and realize the generation of active and reactive power separation control commands.

[0031] Step 3: The power drive unit executes a dynamic phase sequence optimization modulation strategy on the three-phase thyristor array according to the active current drive command amplitude and reactive phase compensation command bias, and in combination with the geometric characteristics of the three-phase load impedance distribution triangle. This generates a dynamically optimized asymmetric trigger phase sequence and implements active modulation and reactive correction, enabling the resistance heating device to achieve adaptive power control under multiple operating conditions.

[0032] In one implementation, the multi-condition resistance heating device first performs the following process in each control cycle: it uses a high-frequency synchronous sampling array to collect the instantaneous voltage and current sampling sequences of the three phases, calculates the instantaneous impedance magnitude sequence, establishes three reference phase axes with an angle of 120 degrees between them centered on the origin in a two-dimensional Euclidean plane coordinate system, determines the impedance characteristic endpoints on each reference phase axis according to the instantaneous impedance magnitude, and connects them to form a three-phase load impedance distribution triangle, determines the load distortion guiding vector based on the three-phase load impedance distribution triangle, and defines the difference between the real-time temperature value of the heating cavity and the target process temperature value as the total power demand radius, thereby constructing a complete dynamic impedance topology distortion model of a three-phase unbalanced load.

[0033] Specifically, the high-frequency synchronous sampling array is configured to simultaneously sample the three-phase voltage and three-phase current of the three-phase power supply. Taking the fundamental frequency of the three-phase power grid as an example, when the fundamental frequency is 50 Hz, the sampling frequency can be set to 10,000 Hz. A sampling frequency 100 times higher than the fundamental frequency allows for a sufficiently dense sequence of instantaneous voltage and current samples within a single power grid cycle, thus accurately characterizing the transient electrical characteristics of the resistance heating device under three-phase unbalanced load conditions. In a specific implementation, 200 sampling points are collected in each power grid cycle, and the control period can be selected as 1 millisecond. In each control cycle, the most recent sampling points are used to form the current sequence of instantaneous voltage and current samples. The high-frequency synchronous sampling array triggers the three-phase voltage and current sampling channels through a unified sampling clock, ensuring strict alignment of the three-phase instantaneous voltage and current samples on the time axis, avoiding errors in calculating the degree of three-phase unbalance due to sampling phase offset.

[0034] After obtaining the instantaneous voltage and current sampling value sequences, for each phase, a point-by-point division operation is performed on the instantaneous voltage and current sampling values ​​at the same sampling time to obtain the instantaneous impedance magnitude sequence. For example, the sampling point number is... The instantaneous voltage sample value is denoted as The instantaneous current sample value is denoted as Then the corresponding instantaneous impedance magnitude can be obtained through calculation. Received, among which Indicates that at sampling point number The instantaneous voltage sample value obtained by sampling the voltage of phase A at any given time, in volts. Indicates that at sampling point number The instantaneous current sample value obtained by sampling the current of phase A at constant intervals, in amperes. Indicates that at sampling point number The instantaneous impedance magnitude of phase A at time A, in ohms. The index is a non-negative integer representing the sampling point. For phases B and C, the instantaneous impedance magnitude sequences can be obtained respectively. and During the calculation, when the absolute value of the instantaneous current sample value is close to zero, the division operation conditions can be limited by setting a current threshold. For example, when... When the absolute value is lower than a preset current threshold, the instantaneous impedance magnitude of the previous sampling point is directly used or the interpolation result is used to prevent numerical divergence. This process ensures that the instantaneous impedance magnitude sequence remains continuous and stable under extremely low load current scenarios, which facilitates subsequent geometric modeling.

[0035] When constructing the geometric representation, three reference phase axes, each at a 120-degree angle to the origin, need to be established in a two-dimensional Euclidean coordinate system. In one implementation, the direction angle of the reference phase axis representing phase A can be set to 0 degrees, the direction angle of the reference phase axis representing phase B to 120 degrees, and the direction angle of the reference phase axis representing phase C to 240 degrees. Taking phase A as an example, in a two-dimensional Euclidean coordinate system, the instantaneous impedance magnitude can be represented by converting from polar coordinates to rectangular coordinates. The transformation relationship between converting points to coordinates in a rectangular coordinate system can be expressed as follows: , ,in This indicates that phase A has a sampling point number of 1. The x-coordinate value corresponding to the time. This indicates that phase A has a sampling point number of 1. The ordinate value corresponding to time 1. This represents the direction angle of the reference phase axis of phase A, in degrees. and These represent the cosine and sine functions, respectively. For phase B and phase C, the direction angle can be used respectively. Degree and The coordinates are obtained by transforming the coordinates of the points in the same way. and .

[0036] In each control cycle, the instantaneous impedance magnitude of the last sampling point within that cycle can be selected as the representative value of the current operating condition. Impedance characteristic endpoints are then calibrated on the reference phase axes of phases A, B, and C according to the radius corresponding to the instantaneous impedance magnitude. This is achieved by connecting the three impedance characteristic endpoints located on the three reference phase axes sequentially with straight line segments, i.e., [the points are then defined as follows]. and points Connect, then put the points and points Connect, and finally the point and points The connection allows for the construction of a three-phase load impedance distribution triangle in a two-dimensional Euclidean coordinate system. When the magnitudes of the three-phase load impedances are completely equal, the three-phase load impedance distribution triangle is an equilateral triangle with three sides of equal length, and its geometric centroid lies precisely at the intersection of the angle bisectors of the three reference phase axes. When the magnitudes of the three-phase load impedances are unequal, the three-phase load impedance distribution triangle undergoes shape distortion. Through the changes in the lengths of the three sides and the shape of the triangle, the degree of three-phase unbalanced load and which phase or two phases have higher impedances can be intuitively presented. Using this geometric representation of the three-phase load impedance facilitates subsequent direct use of the triangle's geometric characteristics for three-phase unbalance analysis and dynamic phase sequence optimization, eliminating the need for repeated complex phasor calculations in subsequent control logic.

[0037] To extract directional features usable for subsequent control from the three-phase load impedance distribution triangle, the geometric centroid of the triangle can be further calculated. The coordinates of the geometric centroid can be calculated by taking the arithmetic mean of the coordinates of the three vertices; for example, the x-coordinate of the geometric centroid can be expressed as... The ordinate of the geometric centroid can be expressed as ,in The x-coordinate represents the geometric centroid of the three-phase load impedance distribution triangle. The ordinate representing the geometric centroid. , , The x-coordinates represent the characteristic endpoints of the impedances of phases A, B, and C, respectively. , , These represent the ordinates of the impedance characteristic endpoints of phases A, B, and C, respectively. The line connecting the origin and the geometric centroid is considered a vector with direction and length; this vector is the load distortion pilot vector. The direction of the load distortion pilot vector reflects which phase or two phases the overall three-phase load impedance distribution is biased towards. For example, when the impedance of phase A is significantly higher than that of phases B and C, the direction of the load distortion pilot vector will be closer to the reference phase axis of phase A. The length of the load distortion pilot vector reflects the degree of triangular distortion. When the three-phase impedances are nearly equal, the geometric centroid is close to the origin, and the length of the load distortion pilot vector is smaller. When the impedance of one phase is much higher than the other two phases, the geometric centroid is biased towards the reference phase axis of that phase, and the length of the load distortion pilot vector increases. This design allows for a quantitative characterization of the directionality and intensity of a three-phase unbalanced load using simple geometric operations without introducing frequency domain transformations or complex phasor calculations. This provides a clear geometric basis for subsequent active and reactive power separation control and dynamic phase sequence optimization.

[0038] refer to Figure 1 , Figure 1 The diagram illustrates the construction process of the three-phase load impedance distribution triangle and load distortion guiding vector in one embodiment. In a two-dimensional Euclidean coordinate system, three reference phase axes are established with an angle of 120 degrees between them, centered at the origin O. The direction angle of the A-phase reference phase axis is set to 0 degrees, extending along the positive direction of the horizontal axis; the direction angle of the B-phase reference phase axis is set to 120 degrees, pointing to the upper left; and the direction angle of the C-phase reference phase axis is set to 240 degrees, pointing to the lower left. In this embodiment, the instantaneous impedance magnitudes of the three phases obtained by the high-frequency synchronous sampling array are as follows: the impedance magnitude of phase A is 3.5 ohms, the impedance magnitude of phase B is 2.8 ohms, and the impedance magnitude of phase C is 2.2 ohms. These values ​​reflect a typical three-phase unbalanced load condition, where the impedance of phase A is significantly higher than that of phases B and C.

[0039] The instantaneous impedance magnitudes of each phase are mapped to a two-dimensional plane using a polar-to-rectangular coordinate conversion. For phase A, the x-coordinate of the impedance characteristic endpoint is calculated as 3.5 multiplied by 0 degrees cosine, which equals 3.5, and the y-coordinate is calculated as 3.5 multiplied by 0 degrees sine, which equals 0. Therefore, the coordinates of point A are (3.5, 0). For phase B, the x-coordinate of the impedance characteristic endpoint is calculated as 2.8 multiplied by 120 degrees cosine, which approximately equals -1.4, and the y-coordinate is calculated as 2.8 multiplied by 120 degrees sine, which approximately equals 2.42. Therefore, the coordinates of point B are approximately (-1.4, 2.42). For phase C, the x-coordinate of the impedance characteristic endpoint is calculated as 2.2 multiplied by 240 degrees cosine, which approximately equals -1.1, and the y-coordinate is calculated as 2.2 multiplied by 240 degrees sine, which approximately equals -1.91. Therefore, the coordinates of point C are approximately (-1.1, -1.91). Figure 1 In the diagram, these three impedance characteristic endpoints are marked with red, green, and blue dots, respectively, and their precise coordinate values ​​are marked near each point.

[0040] By connecting points A, B, and C sequentially with straight line segments, a three-phase load impedance distribution triangle is formed. The three side lengths of this triangle reflect the degree of impedance difference between each phase. In this embodiment, the calculated side length between phase A and phase B is approximately 4.68, labeled LAB; the calculated side length between phase B and phase C is approximately 4.35, labeled LBC; and the calculated side length between phase C and phase A is approximately 4.92, labeled LCA. The side length values ​​are within... Figure 1 The locations of each side are indicated by a label box with a wheat-colored background. Due to the unequal impedance magnitudes of the three phases, the resulting triangle exhibits a distinctly scalene shape, with the vertices of the triangle biased towards the A phase, which has higher impedance. This geometric distortion visually reflects the degree of imbalance in the three-phase load.

[0041] To extract characteristic quantities representing the direction and intensity of unbalance from the three-phase load impedance distribution triangle, it is necessary to calculate the geometric centroid G of the triangle. The x-coordinate of the geometric centroid is obtained by taking the arithmetic mean of the x-coordinates of the three vertices, calculated as (3.5 + -1.4 + -1.1) divided by 3, approximately equal to 0.33; the y-coordinate of the geometric centroid is obtained by taking the arithmetic mean of the y-coordinates of the three vertices, calculated as (0 + 2.42 + -1.91) divided by 3, approximately equal to 0.17. Therefore, the coordinates of the geometric centroid G are approximately (0.33, 0.17). Figure 1 The points are marked with purple squares, and their coordinates are indicated by a light purple background box to the right of each point.

[0042] The line connecting the origin O to the geometric centroid G constitutes the load distortion guiding vector, which in... Figure 1The load distortion pilot vector is clearly marked with a thick red arrow. The length of the load distortion pilot vector reflects the degree to which the three-phase load impedance distribution deviates from a perfectly balanced state. In this embodiment, this length is approximately 0.37, calculated by taking the square root of the sum of the squares of the horizontal and vertical coordinates. The direction angle of the load distortion pilot vector reflects the overall phase direction of the three-phase load impedance. In this embodiment, this direction angle is approximately 27.2 degrees, calculated by dividing the vertical coordinate by the horizontal coordinate, obtaining the arctangent, and converting to degrees. Because the impedance of phase A is significantly higher than the other two phases, its geometric center of gravity is clearly biased towards the reference phase axis of phase A, and the direction of the load distortion pilot vector is close to the 0-degree direction of phase A. Figure 1 The top left corner displays the length and orientation angle parameters of the load distortion guide vector via an information box. Next to this vector, a text box with a yellow background and a red border is labeled "Load Distortion Guide Vector," and a red dashed arrow points from the text box to the vector to ensure clear identification.

[0043] In practical applications, when the three-phase load impedances are nearly equal, the three impedance characteristic endpoints will be distributed on a circle of the same radius, forming a triangle that is close to an equilateral triangle. The geometric center of gravity is close to the origin, and the length of the load distortion pilot vector is close to zero. When the impedance of one or two phases is significantly higher, the shape of the triangle becomes significantly distorted, the geometric center of gravity moves away from the origin, the length of the load distortion pilot vector increases, and its direction points towards the phase with higher impedance. This geometric representation allows for a direct depiction of the three-phase unbalanced load state without complex phasor calculations, using simple coordinate calculations and geometric measurements. This provides a clear geometric basis for subsequent active and reactive power separation control and dynamic phase sequence optimization.

[0044] When constructing the dynamic impedance topology distortion model of a three-phase unbalanced load, it is also necessary to introduce the total power demand radius related to temperature control. This radius is used to map the difference between the real-time temperature of the heating chamber and the target process temperature into a radius quantity in geometric space. The real-time temperature of the heating chamber can be measured by a temperature sensor placed inside the heating chamber or near the heated medium, denoted as [missing information]. The unit is degrees Celsius. The target process temperature is the temperature required to be achieved by the process settings, denoted as . The unit is degrees Celsius. Temperature difference can be defined. ,in This indicates the amount of temperature that needs to be increased. A positive temperature difference indicates that the current temperature is below the target process temperature, requiring continued heating. A near-zero temperature difference indicates that the temperature is close to the target process temperature, allowing for a reduction in heating power. In some implementations, a negative temperature difference can be considered zero or limited to a minimum value to prevent reverse cooling control. To convert the temperature difference into the total power demand radius, a linear mapping relationship can be used, for example, defining the total power demand radius. The relationship with temperature difference is ,in Indicates the radius of total power demand. This represents the scaling factor between the temperature difference and the geometric radius, expressed in units of radius length per degree Celsius. In a specific implementation, if a total power demand radius of 2.0 is desired when the temperature difference is 20 degrees Celsius, this scaling factor can be set. At this point, when the temperature difference is 10 degrees Celsius, the radius of the total power demand is 1.0, and when the temperature difference is 30 degrees Celsius, the radius of the total power demand is 3.0. Through this mapping method, the heating power demand required for the temperature closed loop can be substituted into the two-dimensional Euclidean coordinate system in the form of geometric radii, so that subsequent control can simultaneously consider the three-phase impedance distribution and the total power demand in geometric space.

[0045] To avoid excessively large or small total power demand radius due to temperature differences or sensor errors, upper and lower limits can be introduced based on the proportional mapping in practical implementation. For example, the minimum total power demand radius can be set to 0.1, corresponding to the minimum geometric radius value for maintaining heating; the maximum total power demand radius can be set to 5.0, corresponding to the geometric radius value of the device operating at rated power. When the total power demand radius calculated according to the linear relationship is lower than 0.1, the total power demand radius is limited to 0.1; when the calculated total power demand radius is higher than 5.0, the total power demand radius is limited to 5.0. This ensures that the total power demand radius remains within the range that the control system can effectively handle while maintaining a clear geometric meaning, avoiding overheating or frequent start-stop behaviors.

[0046] In summary, within a complete control cycle, instantaneous voltage and current sampling sequences are obtained through a high-frequency synchronous sampling array. Instantaneous impedance magnitude sequences are formed based on point-by-point division. Three reference phase axes, each at a 120-degree angle to the origin, are established in a two-dimensional Euclidean coordinate system. Impedance characteristic endpoints are calibrated on each reference phase axis and connected to form a three-phase load impedance distribution triangle. Furthermore, the load distortion guiding vector is obtained by calculating the geometric centroid of the three-phase load impedance distribution triangle. The difference between the real-time temperature of the heating cavity and the target process temperature is mapped to the total power demand radius. This allows for the simultaneous characterization of the three-phase unbalanced load state and temperature control requirements within the same geometric space, constructing a dynamic impedance topology distortion model for the three-phase unbalanced load. This dynamic impedance topology distortion model is directly used as input to a vector orthogonal projection interception algorithm based on a virtual rotating coordinate system in subsequent steps, enabling the control algorithm to coordinate the relationship between three-phase imbalance, resistance variation, and temperature requirements within a unified geometric framework.

[0047] In another alternative implementation, the above process can be extended. For example, before calculating the instantaneous impedance magnitude sequence, moving average filtering or finite impulse response filtering can be applied to the instantaneous voltage and current sampled value sequences respectively to suppress grid noise and sensor measurement noise, resulting in a smoother instantaneous impedance magnitude sequence. When establishing the three-phase load impedance distribution triangle, the instantaneous impedance magnitude can be normalized, for example, by dividing the instantaneous impedance magnitude of each phase by the average of the three-phase instantaneous impedance magnitudes, to obtain a dimensionless relative impedance. This makes the shape change of the three-phase load impedance distribution triangle more prominent, facilitating the identification of the direction and degree of three-phase imbalance. Regarding the mapping of the total power demand radius, a piecewise linear function can be used. A smaller proportional coefficient is used when the temperature difference is small to reduce fluctuations during temperature regulation, while a larger proportional coefficient is used when the temperature difference exceeds a certain threshold to provide higher heating power and shorten the heating time in the initial stage of heating. Through these alternative implementations, the adaptability and control performance of the model to different operating conditions can be further optimized without changing the basic structure of the dynamic impedance topology distortion model of the three-phase unbalanced load.

[0048] refer to Figure 3 , Figure 3 This diagram illustrates the time-domain current response waveform of the multi-condition resistance heating device in this embodiment of the invention after implementing an adaptive power control strategy. The specific context of this diagram is an unbalanced operating condition with significant differences in the three-phase load impedances. Phase A is set as a high-impedance load, phase C as a low-impedance load, and phase B as an impedance between the two. Before applying the control strategy of this invention, according to Ohm's law, the current amplitude of phase A will be significantly lower than that of phase C, resulting in uneven heating and severe asymmetry in the three-phase power grid load. Figure 3 The waveform visually reflects the adjustment effect after the controller intervenes. The horizontal axis represents time in milliseconds, covering approximately three complete operating cycles; the vertical axis represents the instantaneous amplitude of the load current in amperes. From Figure 3 The displayed waveform trajectory shows that although the physical impedance characteristics of the three-phase load have not changed, the envelope amplitudes of the three-phase output currents have become highly consistent. The A-phase current waveform shows obvious pulse width broadening characteristics. This is because the controller identifies A-phase as a high-impedance phase and prioritizes the A-phase thyristor to conduct in the voltage peak range through a dynamic phase sequence optimization strategy. It also maximizes the conduction angle based on the active current drive command amplitude, thereby forcibly increasing the effective current output of A-phase to match its energy level with the other two phases.

[0049] In stark contrast, Figure 3Although the amplitude of the current waveform in phase C is similar to that in phase A, its conduction duration is relatively short and the waveform position shows a significant phase shift. This is because phase C, as a low-impedance load, would have excessive current if triggered symmetrically using conventional methods. Therefore, the controller limits the effective conduction range of phase C during the active power modulation phase, while the reactive power correction module applies a specific phase shift to the triggering time of the phase C thyristor based on the reactive power phase compensation command bias. Figure 3 It can be clearly seen that the zero-crossing point of the C-phase current waveform has a certain displacement relative to the standard sinusoidal reference frame. This artificially introduced phase difference generates reactive power opposite to the system's own inductive or capacitive characteristics, thus optimizing the overall power factor of the system while maintaining current amplitude balance. The B-phase current waveform lies between phases A and C, playing a balancing transition role. Furthermore, Figure 3 The current waveform is not a perfect sine wave, but rather exhibits the slicing characteristics typical of thyristor phase-controlled circuits, containing certain high-order harmonic components, which aligns with the physical characteristics of actual industrial environments. The tiny spikes superimposed on the waveform simulate high-frequency noise interference in actual sampling, verifying the robustness of the control algorithm under non-ideal conditions. Figure 3 The time-domain response shows that the method described in this embodiment can quickly respond to the topological distortion of the load impedance within several power grid cycles. By independently and asymmetrically adjusting the firing angle and conduction sequence of the three-phase thyristors, a three-phase current system with symmetrical amplitude is forcibly constructed at the output end. This effectively solves the problem of reduced heating efficiency and power grid pollution caused by load imbalance in resistance heating devices under multiple operating conditions, and achieves accurate tracking of the target process temperature and effective improvement of the power quality on the power grid side.

[0050] In one implementation, after constructing a dynamic impedance topology distortion model of a three-phase unbalanced load, the embedded central processing unit executes a vector orthogonal projection interception algorithm based on a virtual rotating coordinate system in each control cycle. The load distortion guide vector and the total power demand radius are used as inputs. The active current drive command amplitude and reactive power phase compensation command bias are separated geometrically in the synchronous rotating dynamic coordinate system, thereby completing the generation of active and reactive power separation control commands.

[0051] In implementation, a synchronously rotating dynamic coordinate system is first constructed within a two-dimensional Euclidean plane coordinate system. The rotation angle of this system is synchronized with the phase of the fundamental voltage of the power grid. To this end, the embedded central processing unit uses a phase-locked loop algorithm to estimate the instantaneous phase of the fundamental voltage in real time, defining this phase as the power grid phase angle. .in This represents the phase angle synchronized with the grid fundamental voltage, and the unit can be either radians or degrees. In a specific implementation, the phase-locked loop algorithm updates every 0.5 milliseconds. This ensures that the synchronous rotating dynamic coordinate system keeps in line with the phase change of the grid voltage on the time axis.

[0052] In the synchronous rotating dynamic coordinate system, the vertical axis is defined as the active power reference axis, and the horizontal axis is defined as the reactive power reference axis. The direction of the active power reference axis is the same as that of the combined voltage vector of the power grid, and the direction angle is equal to... The direction of the reactive power reference axis is perpendicular to the active power reference axis, and its direction angle is equal to... This setting ensures that the component of the active power reference axis at any point is in phase with the grid voltage, corresponding to active power; while the component of the reactive power reference axis is orthogonal to the grid voltage, corresponding to reactive power. Thus, subsequent projection calculations in the synchronously rotating dynamic coordinate system naturally correspond to the separation of active and reactive components, eliminating the need for conversion between the time and frequency domains.

[0053] After establishing the synchronously rotating dynamic coordinate system, the total power demand radius is used to generate the ideal power output circle. The total power demand radius is denoted as... ,in This represents the geometric magnitude of the combined power target required to meet temperature regulation needs within the current control cycle, and the unit can be any chosen geometric length unit. For example, in one implementation, when the total power demand radius is... This indicates that energy needs to be input into the heating cavity at a level close to the rated power under the current operating conditions. The embedded central processing unit operates in a two-dimensional Euclidean coordinate system, with the origin of a synchronously rotating dynamic coordinate system as the center and a radius... Draw a circle, which is defined as the ideal power output circle. The distance between any point on the ideal power output circle and the origin is equal to the radius of the total power demand. This means that regardless of the direction of the point, the geometric magnitude of the synthesized power is consistent with the temperature demand, the only difference being the ratio between the active and reactive components.

[0054] The load distortion pilot vector, derived from the calculation results of the previous control step, represents the overall offset direction and distortion degree of the current three-phase load impedance in space. The load distortion pilot vector can be represented as a geometric quantity with length and direction, where the length is denoted as . The direction angle is denoted as ,in This represents the geometric length of the load distortion guide vector, reflecting the degree to which the three-phase load impedance distribution deviates from a perfectly balanced state. This represents the direction angle of the load distortion guide vector relative to the horizontal axis of the two-dimensional Euclidean coordinate system. The larger the length, the more unbalanced the three-phase load impedance distribution; the closer the direction is to a certain reference phase axis, the more significant the difference in impedance between the three phases.

[0055] When executing the vector orthogonal projection interception algorithm based on a virtual rotating coordinate system, the load distortion guiding vector needs to be translated into the synchronous rotating dynamic coordinate system. The translation operation does not change the length and direction of the load distortion guiding vector; it only adjusts the vector's starting point from the global coordinate origin to the origin of the synchronous rotating dynamic coordinate system. For ease of calculation, the direction angle of the load distortion guiding vector can be re-recorded in the synchronous rotating dynamic coordinate system as... ,in This indicates the angle representing the direction of load characteristic scanning. In a simple implementation, it can be directly taken as... This involves scanning in a virtual rotating coordinate system along the same direction as the load distortion guide vector. By doing so, the subsequently constructed load characteristic scanning ray will advance along the main direction of the three-phase load impedance distortion, ensuring that the optimal operating balance point of the system simultaneously satisfies the constraints of power demand and load characteristic direction, thus geometrically unifying the load imbalance state with the power demand.

[0056] refer to Figure 2 , Figure 2 This illustration demonstrates the geometric principle and computational process of the vector orthogonal projection interception algorithm based on a virtual rotating coordinate system, as shown in this embodiment of the invention. In this embodiment, the embedded central processing unit first constructs a two-dimensional virtual rotating coordinate system synchronized with the fundamental frequency of the power grid. For example... Figure 2 As shown, this coordinate system comprises two mutually perpendicular axes. The vertical axis is defined as the active power reference axis P, whose direction vector is always locked to and follows the instantaneous phase angle of the grid's synthesized voltage vector. The horizontal axis is defined as the reactive power reference axis Q, whose direction vector lags behind the active power reference axis by 90 degrees. The establishment of this coordinate system relies on phase-locked loop (PLL) technology, ensuring that the rotation speed of the coordinate system is completely consistent with the grid's angular frequency. This transforms a sinusoidal quantity that originally varied with time in a stationary coordinate system into a relatively static or slowly changing quantity in this rotating coordinate system. Figure 2 The dashed circle displayed in the center is defined as the ideal power output circle. The radius R of this circle is determined by the total power demand radius, which is a geometric quantity calculated through linear or nonlinear mapping based on the difference between the real-time temperature sample value of the heating chamber and the target process temperature value. Any point on the ideal power output circle is equidistant from the origin, which geometrically signifies that regardless of the power factor state of the system, the magnitude of its apparent power should meet the current temperature closed-loop control requirements.

[0057] exist Figure 2In the diagram, the ray extending from the origin to the upper right is called the load characteristic scan ray. The direction angle of this ray is determined by the load distortion guide vector, which originates from the geometric centroid offset of the three-phase load impedance distribution triangle constructed by sampling the instantaneous impedance magnitudes of the three phases. The load characteristic scan ray visually indicates the direction of the current three-phase load impedance imbalance in geometric space. For example, when the ray deviates by a specific angle in the first quadrant, it indicates that the impedance of one or two phases is significantly higher than that of the other phases. The load characteristic scan ray and the ideal power output circle are in... Figure 2 There exists a unique geometric intersection point, defined as the system's optimal operating equilibrium point E. Point E has a dual physical significance: firstly, it lies on the ideal power output circle, thus representing an energy intensity that strictly conforms to the heating requirements of temperature control; secondly, it lies on the load characteristic scanning ray, thus its orientation characteristics strictly preserve the impedance distortion information of the current load. To obtain specific control instructions, the processor draws perpendicular lines from point E to both the active power reference axis P and the reactive power reference axis Q, performing vector orthogonal projection operations. Figure 2 The diagram clearly shows the projection line segment of point E onto the active power reference axis P. The length of this line segment corresponds to the active power component projection Mp. After scaling, it directly generates the active current drive command amplitude, which is used to determine the conduction pulse width of the thyristor array to provide the active power required to maintain heating. Simultaneously, the length of the projection line segment of point E onto the reactive power reference axis Q corresponds to the reactive power component projection Mq. The sign and magnitude of this value are mapped to generate the reactive power phase compensation command bias. (The diagram continues...) Figure 2 As shown, if the projection falls on the negative half-axis of the reactive power reference axis, it means that the system needs to introduce a leading or lagging phase shift to generate capacitive or inductive reactive power to offset the power distortion caused by load imbalance. Through this geometric projection method, this embodiment achieves... Figure 2 The described algorithm decouples the generation of active and reactive power control commands, ensuring that the device can adaptively optimize the power quality on the grid side through reactive power compensation while meeting the heating task.

[0058] The load characteristic scanning ray originates from the origin of the synchronously rotating dynamic coordinate system and travels along an angle... Extending in the direction of. To clearly describe the load characteristic scanning ray, coordinate representations can be introduced for any point in the synchronously rotating dynamic coordinate system. Assume the horizontal axis is... The axis, the vertical axis is If the axis is defined, then the load characteristic scanning ray can be expressed in parametric form as follows: ;in The parameter is The x-coordinate of that point at that time. The parameter is The ordinate of that point at that time, This represents the geometric distance from the origin along the direction of the load characteristic scan ray, with units consistent with the total power demand radius. Represents the cosine function. Represents the sine function. Parameters The range of values ​​is That is, only the half-line portion extending outward from the origin is considered.

[0059] The ideal power output circle can be represented by the equation of a circle. The distance from the origin of the synchronously rotating dynamic coordinate system to any point on the ideal power output circle is equal to the radius R of the total power demand. Therefore, the ideal power output circle satisfies the equation... ;in Represents the x-coordinate of any point. R represents the ordinate of any point, and R represents the radius of the total power demand. Represents the square of the x-coordinate. This represents the square of the ordinate. Substituting the parameter representation of the load characteristic scanning ray into the equation of the ideal power output circle, we obtain... ;Right now ;because Therefore there is ; thereby obtaining ;in Take a non-negative value. This result indicates that the load characteristic scanning ray intersects the ideal power output circle exactly at a distance R from the origin. Substituting the expression for the load characteristic scanning ray, the coordinates of the system's optimal operating equilibrium point can be obtained. ; ;in The x-coordinate represents the optimal operating equilibrium point of the system. The vertical coordinate represents the optimal operating equilibrium point of the system. The optimal operating equilibrium point of the system combines two conditions: firstly, the point is located on the ideal power output circle, ensuring that the total power demand radius is met; secondly, the point is located on the load characteristic scanning ray, ensuring that the direction of the equilibrium point is consistent with the load distortion guide vector, reflecting the directional characteristics of the current three-phase unbalanced load.

[0060] After determining the optimal operating equilibrium point of the system, an orthogonal projection needs to be performed on this point in a synchronously rotating dynamic coordinate system, decomposing it onto the active power reference axis and the reactive power reference axis. In the synchronously rotating dynamic coordinate system, the unit direction vector of the active power reference axis can be written as... ;in Represents the unit vector along the active reference axis. Indicates Let cosine be the value of the angle. Indicates Let be the sine of the angle. The unit direction vector of the reactive power reference axis is orthogonal to the active power reference axis, and can be written as... ;in Represents the unit vector along the reactive power reference axis. Indicates The values ​​are the negative and positive sines of the angle. Indicates Let be the cosine of the angle.

[0061] The projection length of the system's optimal operating equilibrium point onto the active power reference axis can be obtained through vector dot product. ;in This represents the geometric projection length of the system's optimal operating equilibrium point along the active power reference axis, with units identical to the total power demand radius. The projection length of the system's optimal operating equilibrium point along the reactive power reference axis can be written as... ;in It represents the geometric projection length of the system's optimal operating equilibrium point along the reactive power reference axis. The sign indicates the intensity of the active component that is in the same or opposite direction as the grid voltage. The positive and negative values ​​correspond to the directions of reactive components that lead or lag the grid voltage, respectively.

[0062] To obtain the control quantity from the geometric projection length, an amplitude mapping relationship needs to be introduced. An active current drive proportional coefficient can be defined. and reactive phase compensation ratio coefficient The active current drive command amplitude is denoted as... The reactive phase compensation command offset is denoted as Then the following mapping can be used. ; ;in This indicates the active current drive command amplitude, in amperes. This represents the proportionality coefficient from geometric length to current value, expressed in amperes per unit geometric length. The reactive phase compensation command offset can be expressed in angle or electrical angle. This represents the scaling factor from geometric length to electrical angular offset, expressed in units of "angle value per unit geometric length". For example, when Amperes per unit length Then there is Ampere indicates the target active current that should be generated in each phase control loop with an amplitude of 2 amperes; when Degree per unit length, Then there is The degree indicates that the phase needs to be compensated by 2 degrees in advance in subsequent trigger control to form an appropriate capacitive reactive power cancellation effect.

[0063] The significance of this mapping method lies in the fact that the location of the optimal operating equilibrium point of the system in geometric space is simultaneously constrained by the total power demand radius and the direction of the load distortion guiding vector. The projection length of the point on the active power reference axis directly reflects the intensity of the active power component required to meet the current temperature requirements, while the projection length of the point on the reactive power reference axis reflects the reactive power component that needs to be generated to improve the three-phase unbalanced state and the reactive power distribution on the grid side, under the premise of meeting the temperature requirements. and Two coefficients can convert the projected length, which has a clear geometric meaning, into specific control commands that can be directly applied to the current control loop and the trigger phase control loop. The active current drive command amplitude is used in the subsequent current regulation loop to drive the resistive heating device to output the corresponding active power, and the reactive phase compensation command bias is used in the subsequent phase control to adjust the thyristor trigger phase position and regulate the reactive power flow on the grid side.

[0064] In one specific embodiment, the sampling period is 1 millisecond, and the total power demand radius varies from 0.5 to 3.0. The length of the load distortion pilot vector is [not specified in the original text]. The length is relatively small, and its direction is close to the angle bisector of the three reference phase axes. At this time, the load characteristic scanning ray intersects the ideal power output circle almost along the three-phase equilibrium direction, and the projection length of the system's optimal operating equilibrium point on the active power reference axis direction is... Approximately the radius of total power demand, while the projected length along the reactive power reference axis. Approaching zero, the amplitude of the active current drive command after mapping is relatively large, while the offset of the reactive phase compensation command is close to zero, and the control behavior is close to pure active heating. When the three-phase load impedance is severely unbalanced, the direction of the load distortion guide vector is significantly biased towards the phase with larger impedance, and the load characteristic scanning ray extends in the skewed direction. The final projection length of the optimal operating equilibrium point of the system on the reactive reference axis is... The reactive power will increase significantly, and the offset of the reactive phase compensation command after mapping will also increase accordingly. Subsequent trigger control will adjust the reactive power by more obvious phase advance or phase delay, so as to make the amplitude and phase distribution of the three-phase current more balanced while meeting the total power demand radius.

[0065] In another alternative implementation, the load distortion guide vector can be angularly corrected before calculating the optimal operating equilibrium point of the system. For example, an angular correction amount can be introduced. Set the scan direction to ,in This indicates an angular offset introduced based on experience or a preset strategy, used to further bias towards a direction favorable to the current balance of two phases when the load is severely unbalanced. In this case, the load characteristic scanning ray no longer strictly follows the direction of the load distortion guiding vector, but is finely adjusted based on it, thereby enhancing the adaptability to specific operating conditions while maintaining overall load information. Furthermore, after obtaining the active current drive command amplitude and reactive phase compensation command offset, a first-order inertial filter or moving average filter can be introduced in time to make the control command changes smoother, avoiding excessively rapid phase adjustments under load abrupt changes or grid disturbances, thereby improving the stability of the entire resistance heating device during multi-condition switching.

[0066] In one implementation, after calculating the load distortion guide vector and the total power demand radius, the control process enters the dynamic phase sequence optimization modulation strategy stage. At this time, the power drive unit has obtained the active current drive command amplitude and reactive phase compensation command bias, and retains the geometric information of the three-phase load impedance distribution triangle in the two-dimensional Euclidean coordinate system. Within each AC grid cycle, the power drive unit dynamically adjusts the triggering sequence and triggering angle of the three-phase thyristor array based on the above information, forming a dynamically optimized asymmetric triggering phase sequence. Under this triggering phase sequence, it sequentially performs phase sequence reorganization, active power modulation, and reactive power correction, enabling the resistance heating device to stably output the desired active power under three-phase unbalanced load and multi-condition operation, while simultaneously improving the reactive power distribution and current balance on the grid side.

[0067] First, phase sequence reordering is accomplished based on the geometric characteristics of the three-phase load impedance distribution triangle. The three vertices of the three-phase load impedance distribution triangle correspond to the impedance characteristic endpoints of phases A, B, and C, respectively. The coordinates of these three vertices in the two-dimensional Euclidean coordinate system are denoted as follows: , and .in, The x-coordinate represents the characteristic endpoint of phase A impedance. The ordinate represents the characteristic endpoint of phase A impedance. and The x and y coordinates represent the characteristic endpoints of phase B impedance, respectively. and Let x and y represent the x and y coordinates of the characteristic endpoint of phase C's impedance, respectively. The three sides of the three-phase load impedance distribution triangle connect phase A to phase B, phase B to phase C, and phase C to phase A. The lengths of the three sides can be calculated using distance formulas; for example, the side length between phase A and phase B can be written as... ;in This represents the length of the side connecting the characteristic impedance endpoints of phase A and phase B. To represent the square root operation, This represents the square of the difference in the x-coordinates. This represents the square of the difference in the ordinates. Similarly, we can obtain... ; ;in This represents the length of the side connecting the characteristic impedance endpoints of phase B and phase C. This indicates the length of the side connecting the characteristic endpoints of phase C and phase A impedances.

[0068] In one implementation, the power drive unit controls the power supply in each control cycle. , and Compare the lengths of the three sides and sort them according to their numerical values. Let the lengths of the three sides after sorting be _____. , and ,in This represents the longest side among the three sides. This represents the side with the shortest length among the three sides. This represents an edge that lies between two points. (and) The corresponding two phases are defined as high-impedance phase pairs, and The corresponding two phases are defined as low-impedance phase pairs, and The corresponding two phases are defined as a medium impedance phase pair. For example, in a certain control cycle, if... , , (The unit is any chosen geometric unit of length), then we have The corresponding high-impedance phase pairs are phase A and phase B; The corresponding low-impedance phase pairs are phase C and phase A; The corresponding intermediate impedance phase pairs are phase B and phase C.

[0069] The rationale behind this division is that the larger the side length of the three-phase load impedance distribution triangle, the farther the distance between the characteristic endpoints of the corresponding two phases on the geometric plane, reflecting a more significant difference in impedance magnitude or relative impedance change trend between the two phases. High-impedance phase pairs have significant differences between their corresponding phases, which can easily cause uneven current distribution or deviate the desired phase angle in a three-phase circuit. If high-impedance phase pairs are prioritized for conduction in the triggering sequence and provided with a more favorable voltage range, the unfavorable factors of high-impedance phase pairs in static impedance can be compensated for to some extent, making the overall current distribution closer to the target equilibrium state. Low-impedance phase pairs have the shortest distance between their corresponding characteristic endpoints, and the two phases have similar impedance levels, inherently possessing good current carrying capacity. Therefore, their triggering sequence can be appropriately shifted forward or backward without causing excessive negative impact on the overall power balance.

[0070] After obtaining the high-impedance, medium-impedance, and low-impedance phase pairs, the power drive unit adjusts the conduction sequence of the three-phase thyristor array in subsequent AC grid cycles, forming a dynamically optimized asymmetric triggering phase sequence. Taking a grid frequency of 50 Hz as an example, a complete cycle is 20 milliseconds. In three-phase control, this cycle is usually divided into multiple phase intervals, such as every 60 degrees, corresponding to a time length of approximately 3.33 milliseconds. In a traditional symmetrical triggering phase sequence, the thyristors of phases A, B, and C conduct in a fixed order within their respective phase intervals, with a strict 120-degree difference in the conduction interval between the three phases. The entire triggering sequence repeats within each cycle, constituting symmetrical triggering. The dynamically optimized asymmetric triggering phase sequence breaks this fixed order, appropriately advancing the triggering time of the thyristors belonging to the high-impedance phase pairs and appropriately delaying the triggering time of the thyristors belonging to the low-impedance phase pairs. This allows the high-impedance phase pairs to obtain a larger effective conduction window within a cycle, thereby injecting more active current into the high-impedance phase pairs without changing the total power demand radius.

[0071] For example, if within a certain cycle, the high-impedance phase pair is phases A and B, the low-impedance phase pair is phases C and A, and the medium-impedance phase pair is phases B and C, then the originally symmetrical trigger sequence A, B, C can be adjusted to B, A, C. Alternatively, it can be further subdivided into preferentially triggering the three-phase thyristor array channels corresponding to phases A and B near the voltage peak, allowing the high-impedance phase pairs to obtain more conduction time in the region with higher combined voltage. The effect of this is that the effective voltage waveform area obtained by the high-impedance phase pairs during conduction increases, and under the same total power demand radius, the current increase of the high-impedance phase pairs is more significant, which helps to compensate for the adverse effects of their larger static impedance. At the same time, the low-impedance phase pairs conduct in the lower voltage or shorter range; although the impedance of these phases is inherently smaller, the shorter conduction window can suppress excessive current, reducing the risk of overload and overheating.

[0072] After dynamic phase sequence optimization is completed, active power modulation is carried out under the dynamically optimized asymmetric triggering phase sequence. At this time, the active current drives the command amplitude. This has already been calculated in the previous step. This represents the target amplitude of the equivalent active current in the three-phase system, expressed in amperes, to meet the temperature control requirements corresponding to the total power demand radius within the current control cycle. In the control of a three-phase thyristor array, a combination of phase control and pulse width modulation can be used to achieve precise tracking of the active current drive command amplitude.

[0073] In a specific implementation, the control cycle of each phase is divided into several smaller conduction sub-intervals. The length of each sub-interval can be between 0.5 milliseconds and 1 millisecond, selected according to the switching frequency capability of the actual hardware. Within each sub-interval, a single channel of the three-phase thyristor array is either in the on state or in the off state. To simplify the design, it can be assumed that the grid voltage change is small within a single conduction sub-interval, and the voltage waveform within that sub-interval can be considered approximately constant. Thus, the active power transmitted to the load within that sub-interval is approximately proportional to the conduction time. In this way, active power modulation can be transformed into determining the number of effective conduction sub-intervals for each phase within one grid cycle, so that the overall transmitted active power matches the target active power calculated from the active current drive command amplitude.

[0074] If the total number of conducting sub-intervals used for active power modulation within a power grid cycle is denoted as... ,in This represents the number of conducting sub-intervals used as control units within one cycle, and is a positive integer, such as 120, corresponding to a sub-interval length of approximately 0.167 milliseconds. For a three-phase system, it can be... The actual number of conducting sub-intervals allocated to each phase (A, B, and C) within one cycle is denoted as follows: , and These three numbers satisfy ;in This indicates the number of conducting sub-intervals of phase A within one cycle. This indicates the number of conducting sub-intervals of phase B within one cycle. This indicates the number of conducting sub-intervals of phase C within one cycle. By promoting dynamically optimized asymmetric triggering phase sequence, the conducting sub-intervals of phases containing high-impedance phase pairs can be preferentially allocated to moments with higher voltage amplitudes, and the number of conducting sub-intervals of these phases can be set slightly higher than the average level. For example, under a certain operating condition, it can be set... , , In this system, phases A and B together form a high-impedance phase pair, and the sum of the number of conducting sub-intervals in one cycle is significantly higher than that of phase C. Thus, the effective conduction time of the high-impedance phase pair is extended within one cycle. Combined with a higher voltage range, this allows for a current amplitude closer to the active current drive command amplitude. Meanwhile, the conduction time of the phase corresponding to the low-impedance phase pair is shortened, which helps suppress excessive current.

[0075] In the design process of active power modulation, the relationship between the active current drive command amplitude and the conduction sub-interval allocation scheme can be established in advance. For example, for different The equivalent active current amplitude under each combination of conducting sub-intervals is calculated offline, taking into account the actual grid voltage and load impedance levels, and a lookup table is created based on this. During operation, the power drive unit selects the conducting sub-interval allocation scheme closest to the target from the lookup table according to the current active current drive command amplitude. Then, based on the classification results of high-impedance phase pairs, medium-impedance phase pairs, and low-impedance phase pairs, the allocation of conducting sub-intervals among the three phases is fine-tuned. This method of offline table lookup combined with online fine-tuning utilizes accurate pre-calculated data, reducing the real-time computation burden, while retaining the adaptive capability of the dynamic phase sequence optimization modulation strategy for three-phase unbalanced loads.

[0076] After active power modulation is completed, reactive power compensation is further performed based on dynamically optimized asymmetric triggering phase sequence and conduction sub-interval allocation. The reactive power phase compensation command offset is denoted as... ,in This represents the phase offset introduced to adjust the reactive power distribution of the three-phase system within the current control cycle. It can be expressed in electrical degrees. The sign and size come from the projection result in the previous step, when When the value is positive, it means that the current position of the overall system in geometric space suggests the use of hysteresis compensation, that is, generating more inductive reactive power by delaying the conduction; when When the value is negative, it means that it is recommended to use advanced compensation to generate more capacitive reactive power by turning on the circuit in advance.

[0077] For any phase in a three-phase thyristor array, its reference firing angle can be defined as: ,in Indicates phase, and can take values ​​of A, B, or C. This represents the firing angle of the thyristor in this phase relative to zero voltage within one grid cycle, without considering reactive power phase compensation. To perform reactive power correction, a reactive power phase compensation command bias can be superimposed on the reference firing angle to obtain the actual firing angle. ;in Indicates phase as The actual firing angle of the thyristor after considering reactive power correction, in degrees. This is the phase correction coefficient, and its value can be... , or For example, for two phases that form a high-impedance phase pair, it can be... Set as This shifts the firing angle of both phases backward, causing the current waveform to lag behind the voltage waveform within a cycle. This increases the inductive reactive power component while transferring active power to the load, helping to suppress current distortion caused by high impedance. For two phases forming a low-impedance phase pair, this can... Set as This causes the firing angle to move forward, generating a certain amount of capacitive reactive power by turning on the circuit earlier, thus offsetting some of the inductive reactive power present in the system. For a phase in a medium-impedance phase pair, this can... Set as It keeps its firing angle near the reference value and is mainly responsible for the transmission of active power.

[0078] refer to Figure 4 , Figure 4 The diagram illustrates firing angle modulation under dynamic phase sequence optimization in one embodiment. It comprises two sub-graphs, showing the baseline firing angle state and the firing angle modulation state after reactive phase compensation, respectively. The horizontal axis represents electrical angles in degrees, ranging from 0 to 360 degrees, corresponding to a complete AC power grid cycle. The vertical axis represents the normalized voltage amplitude, ranging from -1.5 to +1.8. Figure 4 The upper sub-icon is labeled as (a) symmetrical triggering with reference firing angle and no phase compensation. Figure 4 The sub-icon at the bottom is labeled (b) Dynamic phase sequence optimization modulation with reactive phase compensation.

[0079] In sub-figure (a), the three-phase voltage waveforms are plotted. The phase A voltage waveform is represented by a solid red line, with its peak value appearing around 90 degrees. The phase B voltage waveform is represented by a solid green line, lagging behind phase A by 120 degrees, with its peak value appearing around 210 degrees. The phase C voltage waveform is represented by a solid blue line, lagging behind phase A by 240 degrees, with its peak value appearing around 330 degrees. In symmetrical triggering mode, the reference trigger angles of the three-phase thyristors are set as follows: phase A reference trigger angle is 90 degrees, phase B reference trigger angle is 210 degrees, and phase C reference trigger angle is 330 degrees. These three trigger angles are strictly 120 degrees apart on the time axis, forming a traditional symmetrical triggering phase sequence. In sub-figure (a), the positions of the three reference trigger angles are marked with vertical dashed lines in red, green, and blue, respectively. A downward-pointing triangle is drawn where the dashed lines intersect the horizontal axis, and the reference trigger angle values ​​for each phase are labeled above the triangles using text boxes with colored backgrounds. In symmetrical triggering mode, the reactive phase compensation command bias is 0, and each phase thyristor is turned on strictly according to the reference triggering angle, without any phase advance or delay adjustment action.

[0080] In sub-figure (b), the three-phase voltage waveforms are also drawn, and the waveform style is consistent with that in sub-figure (a). However, in this embodiment, the reactive phase compensation command bias calculated according to the aforementioned steps is -12 degrees. The negative value indicates that the system needs to generate a capacitive reactive power cancellation effect by triggering in advance to improve the three-phase reactive power distribution. According to the dynamic phase sequence optimization modulation strategy, the three phases adopt different phase correction coefficients. As one of the members of the high-impedance phase pair, phase A has a phase correction coefficient set to positive 1, and the actual trigger angle is calculated as the reference trigger angle plus 1 times the reactive phase compensation command bias, that is, 90 degrees plus 1 multiplied by -12 degrees equals 78 degrees. The phase correction coefficient of phase B is set to positive 0.5, and the actual trigger angle is calculated as 210 degrees plus 0.5 multiplied by -12 degrees equals 204 degrees. As one of the members of the low-impedance phase pair, phase correction coefficient is set to negative 1, and the actual trigger angle is calculated as 330 degrees plus -1 multiplied by -12 degrees equals 342 degrees.

[0081] In subgraph (b), the reference trigger angle position is marked with a light-colored vertical dotted line to show the original trigger time as a reference. The optimized actual trigger angle position is marked with a thicker vertical dashed line. A downward-pointing triangle is drawn where the dashed line intersects the horizontal axis. Above the triangle, a text box with a colored background indicates the actual trigger angle value of each phase. It can be observed that the actual trigger angle of phase A, 78 degrees, is shifted forward by 12 degrees relative to the reference trigger angle of 90 degrees, and the actual trigger angle of phase C, 342 degrees, is shifted backward by 12 degrees relative to the reference trigger angle of 330 degrees. The trigger time adjustment directions of these two phases are opposite. Near the trigger angles of phase A and phase C, bidirectional arrows are drawn to indicate the phase offset. The two ends of the arrows connect the reference trigger angle position and the actual trigger angle position. Below the arrows, a purple text box indicates the offset calculation relationship. For example, phase A is marked as having an offset of -12 degrees equal to 1 times the reactive power phase compensation command, and phase C is marked as having an offset of -1 times the reactive power phase compensation command, which is equal to +12 degrees.

[0082] Regarding specific numerical settings, limitations can be imposed. The absolute value does not exceed a certain maximum allowable value, for example... ,in This indicates that the maximum allowable offset angle is 15 degrees. When the calculated... When the current exceeds this range, it can be truncated at the boundary value to avoid excessive phase adjustment causing severe distortion of the current waveform or frequent high voltage loads on the thyristor. Impact. Through the above method, an appropriate phase bias is superimposed on the natural zero-crossing trigger moment of each phase's thyristors to achieve reactive power correction. A positive bias corresponds to a trigger moment shifted backward along the voltage waveform direction, forming a more lagging current, and the corresponding equivalent circuit exhibits stronger inductive characteristics; a negative bias corresponds to a trigger moment shifted forward, forming a relatively leading current, and the corresponding equivalent circuit exhibits stronger capacitive characteristics. Thus, under the coverage of the entire dynamic phase sequence optimization modulation strategy, active power modulation is responsible for meeting temperature-related energy demands, while reactive power correction is responsible for shaping the electrical presentation of the three-phase system to the grid, making the distribution of apparent power more balanced.

[0083] In another alternative implementation, to avoid frequent phase sequence switching due to slight fluctuations in the three-phase load impedance distribution, a hysteresis judgment can be introduced before performing phase sequence reconfiguration. For example, a threshold value for the difference in side length can be set. ,when Less than At this time, instead of reclassifying high-impedance phase pairs and low-impedance phase pairs, the classification results from the previous cycle are used; only when Greater than Only when the phase sequence changes is the corresponding phase of the high-impedance phase pair, low-impedance phase pair, and medium-impedance phase pair updated. This avoids the dynamic phase sequence optimization modulation strategy from frequently adjusting the trigger sequence when the three-phase load impedance changes slightly, thereby reducing the switching impact of the three-phase thyristor array under unnecessary operating conditions and improving the overall reliability of the resistance heating device.

[0084] Through the aforementioned dynamic phase sequence optimization modulation strategy, the active current drive command amplitude and reactive phase compensation command bias are transformed into specific trigger sequences and trigger angle control, realizing adaptive power control of the resistance heating device under multiple operating conditions: the three-phase load impedance distribution triangle provides geometric information on three-phase unbalance, the load distortion guiding vector and the total power demand radius constitute power demand constraints in geometric space, the vector orthogonal projection interception algorithm based on the virtual rotating coordinate system gives the active current drive command amplitude and reactive phase compensation command bias, and the dynamic phase sequence optimization modulation strategy applies this geometric and electrical information to the triggering behavior of the three-phase thyristor array, forming a complete closed-loop control link from impedance topology to current waveform to power balance.

[0085] The present invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method of adaptive power control for a multi-mode resistive heating device, characterized in that, The method comprises: Step one: using a high-frequency synchronous sampling array to collect three-phase instantaneous voltage sample value sequences and instantaneous current sample value sequences, calculate instantaneous impedance modulus value sequences, establish three reference phase axes that are mutually at an angle of 120 degrees with the coordinate origin as the center in a two-dimensional Euclidean plane coordinate system, determine impedance characteristic end points on each reference phase axis according to the instantaneous impedance modulus values, and connect the three impedance characteristic end points on the three reference phase axes to form a three-phase load impedance distribution triangle, determine a load distortion guide vector based on the three-phase load impedance distribution triangle, and define the difference between the real-time temperature value of the heating cavity and the target process temperature value as a total power demand radius, thereby constructing a dynamic impedance topology distortion model of a three-phase unbalanced load; Step two: introducing the load distortion guide vector and the total power demand radius into a vector orthogonal projection intercept algorithm based on a virtual rotating coordinate system, determining a system optimal operation balance point by orthogonal projection using a synchronous rotating dynamic coordinate system, generating an active current drive instruction amplitude and a reactive phase compensation instruction bias, and realizing generation of active and reactive separation control instructions; Step three: a power drive unit executes a dynamic phase sequence optimization modulation strategy on a three-phase thyristor array according to the active current drive instruction amplitude and the reactive phase compensation instruction bias and in combination with the geometric characteristics of the three-phase load impedance distribution triangle, generates a dynamically optimized asymmetric trigger phase sequence, and implements active modulation and reactive correction, so that the resistance heating device realizes adaptive power control under multiple working conditions.

2. The adaptive power control method for multi-condition resistance heating apparatus according to claim 1, wherein, In step one, the high-frequency synchronous sampling array is arranged at the input end of the heating device power supply, and the three-phase line is synchronously sampled at a fixed sampling period within a single working condition cycle to obtain three-phase instantaneous voltage sample value sequences and instantaneous current sample value sequences, and point-by-point division is performed on the instantaneous voltage sample value and the instantaneous current sample value of each phase to generate the corresponding instantaneous impedance modulus value sequence.

3. The adaptive power control method for multi-condition resistance heating apparatus according to claim 2, wherein, In step one, in the two-dimensional Euclidean plane coordinate system, three reference phase axes that are mutually at an angle of 120 degrees with the coordinate origin as the center are established for the A phase, the B phase, and the C phase, respectively, and impedance characteristic end points are marked on each reference phase axis according to the current value in the instantaneous impedance modulus value sequence of the corresponding phase, and the three impedance characteristic end points on the three reference phase axes are sequentially connected by straight line segments to form a three-phase load impedance distribution triangle.

4. The adaptive power control method for multi-condition resistance heating apparatus according to claim 3, wherein, In step one, the arithmetic mean of the coordinates of the three vertices of the three-phase load impedance distribution triangle is calculated to obtain the geometric center of the three-phase load impedance distribution triangle, the line connecting the coordinate origin and the geometric center is defined as the load distortion guide vector, and the total power demand radius is determined based on the difference between the real-time temperature value of the heating cavity collected by the temperature sensor and the target process temperature value, and the load distortion guide vector and the total power demand radius are used as parameters of the dynamic impedance topology distortion model of the three-phase unbalanced load.

5. The adaptive power control method for multi-condition resistance heating apparatus according to claim 4, wherein, In step two, the vector orthogonal projection intercepting algorithm based on the virtual rotating coordinate system is executed by the embedded central processor, the embedded central processor constructs a synchronous rotating dynamic coordinate system in a two-dimensional Euclidean plane coordinate system by using angle information synchronized with the fundamental frequency of the power grid, defines the longitudinal axis of the synchronous rotating dynamic coordinate system as the active reference axis, and defines the transverse axis perpendicular to the active reference axis as the reactive reference axis.

6. The adaptive power control method for multi-condition resistance heating apparatus according to claim 5, wherein, In step two, the embedded central processor draws an ideal power output circle with the origin of the synchronous rotating dynamic coordinate system as the center and the total power demand radius as the radius, translates the load distortion guide vector to obtain a distortion reference vector in the synchronous rotating dynamic coordinate system, and draws a load characteristic scanning ray from the origin of the synchronous rotating dynamic coordinate system in the direction of the distortion reference vector, and determines the geometric intersection point of the load characteristic scanning ray and the ideal power output circle as the system optimal operation balance point.

7. The adaptive power control method for multi-condition resistance heating apparatus according to claim 6, wherein, In step two, the embedded central processor draws an ideal power output circle with the origin of the synchronous rotating dynamic coordinate system as the center and the total power demand radius as the radius, translates the load distortion guide vector to obtain a distortion reference vector in the synchronous rotating dynamic coordinate system, and draws a load characteristic scanning ray from the origin of the synchronous rotating dynamic coordinate system in the direction of the distortion reference vector, and determines the geometric intersection point of the load characteristic scanning ray and the ideal power output circle as the system optimal operation balance point.

8. The adaptive power control method for multi-condition resistance heating apparatus according to claim 7, wherein, In step three, the dynamic phase sequence optimization modulation strategy includes phase sequence recombination, active modulation and reactive correction. In phase sequence recombination, the power driving unit calculates the lengths of three sides of a three-phase load impedance distribution triangle, sorts the lengths according to their numerical values, selects two vertices corresponding to the longest length as the high impedance phase pair, selects two vertices corresponding to the shortest length as the low impedance phase pair, and sets the trigger sequence of the three-phase thyristor array in the subsequent alternating current grid cycle according to the order of high impedance phase pair first and low impedance phase pair later, to form a dynamically optimized asymmetric trigger phase sequence.

9. The adaptive power control method for multi-condition resistance heating apparatus according to claim 8, wherein, In the active modulation process in step three, the power driving unit uses the pulse width modulation technology to intercept the voltage waveform corresponding to the active current driving instruction amplitude in the conduction interval of each phase thyristor under the dynamically optimized asymmetric trigger phase sequence, to meet the heating power demand reflected by the total power demand radius.

10. The adaptive power control method for multi-condition resistance heating apparatus according to claim 9, wherein, In the reactive power correction process in step three, the power drive unit superimposes a reactive phase compensation instruction bias on the basis of the natural zero-crossing trigger time of each phase thyristor, and when the reactive phase compensation instruction bias is positive, the trigger time of the thyristor is shifted backward along the voltage waveform direction to produce an inductive reactive power offset effect, and when the reactive phase compensation instruction bias is negative, the trigger time of the thyristor is shifted forward along the voltage waveform direction to produce a capacitive reactive power offset effect, so as to improve the distribution of reactive power of each phase while executing the dynamic phase sequence optimization modulation strategy.

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