Temperature-based variable step size MPPT method for temperature difference heat and power cogeneration

Abstract

The application discloses a temperature-based variable step MPPT method for temperature difference combined heat and power, and belongs to the field of temperature difference power generation. The method is realized as follows: a curve graph of output power and output voltage of a thermoelectric sheet is measured; a temperature difference is formed between the thermoelectric sheet by high-temperature gas and cooling water, a potential difference is generated, and electric energy is outputted outward; the voltage, current and the temperature of the hot and cold ends of the thermoelectric sheet are collected, the power at the moment is calculated, the power at the moment is subtracted from the power calculated at the last moment to obtain dp, the voltage at the moment is subtracted from the voltage collected at the last moment to obtain dv, dp / dv at the moment is calculated, and A is obtained by multiplying dp / dv at the moment with dp / dv calculated at the last moment; the step is calculated according to the curve graph and the positive and negative conditions of dp / dv at the moment; and the duty cycle is regulated according to the obtained step, so that the MPPT control is realized. The step disturbance factor based on the temperature difference is added, the relevant characteristics of the inverse tangent function in the corresponding interval are combined, and the real-time reasonable self-adaptive adjustment of the MPPT step is realized.

Description

Technical Field

[0001] This invention relates to the control of the output power of a combined heat and power system based on thermoelectric power generation technology, and more particularly to a variable step size MPPT method based on temperature change for regulating the output power of a thermoelectric power system. This method is applicable to the working process of a thermoelectric power generation system and belongs to the field of thermoelectric power generation. Background Technology

[0002] Energy shortage is a major challenge facing the world today, and energy conservation and efficiency improvement have become core themes of industrial development. Thermoelectric power generation technology is a technology that directly converts heat energy into electrical energy based on semiconductor thermoelectric materials. However, due to material limitations, the thermoelectric conversion efficiency of thermoelectric power generation technology is relatively low, and the output fluctuates significantly with changes in input conditions. To address the problem of low thermoelectric conversion efficiency in thermoelectric power generation technology, the MPPT method is used at the output end of the thermoelectric power generation system to stabilize the output electrical energy near the maximum power point.

[0003] The MPPT method allows the power generation system to operate continuously at its maximum power point, and its control effect directly impacts the system's performance. While commonly used MPPT algorithms are simple and easy to implement, they suffer from low tracking accuracy due to step size selection issues when adjusting the duty cycle. Furthermore, for thermoelectric power generation systems, the output is affected by the temperature difference between the hot and cold ends, and current MPPT algorithms do not consider the relationship between the perturbation step size and the temperature difference. Therefore, a temperature-based variable-step MPPT method that takes into account the temperature difference is needed. Summary of the Invention

[0004] To address the issues of low output power and fluctuating operating conditions in thermoelectric power generation systems (TECS), the MPPT algorithm is needed to stabilize its operating state at the maximum power point. The main objective of this invention is to provide a temperature-based variable-step MPPT method for thermoelectric cogeneration. This method controls the output power of the thermoelectric power generation system, ensuring it always operates at its maximum power point. Since the output power of the thermoelectric power generation system is related to the temperature difference across the thermoelectric generator, a temperature-difference-based step-size perturbation factor is incorporated. Combined with the correlation characteristics of the arctangent function in the corresponding interval, real-time and adaptive adjustment of the MPPT step size is achieved, thus realizing a temperature-based variable-step MPPT method for thermoelectric power generation systems.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention discloses a temperature-based variable-step MPPT method for thermoelectric cogeneration, implemented based on a thermoelectric cogeneration system. The thermoelectric cogeneration system includes a collector, a radiator, and a thermoelectric element. High-temperature gas is introduced into the collector, and cooling water is introduced into the radiator. A thermoelectric element is sandwiched between the collector and the radiator, creating a temperature difference that outputs electrical energy. The MPPT controller collects the temperatures of the hot and cold ends of the thermoelectric element and calculates the temperature difference. Based on the temperature, it calculates a temperature disturbance factor and substitutes relevant parameters into an arctangent function to calculate the base step size. Since MPPT control changes the output voltage by altering the duty cycle of the DC-DC converter, thereby stabilizing the operating point near the maximum power point, the duty cycle is changed according to the calculated disturbance step size to achieve real-time adjustment of the output voltage, realizing MPPT control of the thermoelectric power generation system.

[0007] The temperature-based variable step size MPPT method for thermoelectric cogeneration includes the following steps:

[0008] Step 1: Measure the output power and output voltage curves of the thermoelectric element; a temperature difference is formed between the high-temperature gas and the cooling water at both ends of the thermoelectric element, generating a potential difference and outputting electrical energy.

[0009] Step 2: Collect the voltage and current of the electrical energy mentioned in Step 1, as well as the temperature of the hot and cold ends of the thermoelectric element;

[0010] Step 3: Based on the voltage and current collected in Step 2, calculate the power at this time, and subtract the power at this time from the power calculated at the previous moment to get dp. Subtract the voltage at this time from the voltage collected at the previous moment to get dv. Calculate dp / dv at this time, and multiply dp / dv at this time with dp / dv calculated at the previous moment to get A.

[0011] Step 4: Calculate the step size based on the curve from Step 1 and the sign of dp / dv at this point in Step 3.

[0012] Step 4.1: Introduce the arctangent step size function u(x) and the temperature perturbation factor λ. i ;

[0013]

[0014] λ i =ε i (1+f(T h ,ΔT)) i=1,2,3 (2)

[0015]

[0016] d i =u(x)·λ i i = 1, 2, 3 (4)

[0017] Where a is the step size scaling parameter, x is the independent variable of the arctangent step size function, and ε i T is the step size factor. h T represents the hot end temperature of the thermoelectric element. hmax ΔT represents the maximum temperature that the hot end of the thermoelectric element can withstand, and ΔT is the temperature difference between the hot and cold ends of the thermoelectric element. max To ensure the maximum temperature difference that the hot and cold ends of the thermoelectric element can withstand;

[0018] Step 4.2: If the dp / dv obtained in Step 3 is greater than zero, it indicates that the maximum power point is to the right of the current point; determine the sign of A. When A is greater than zero, it indicates that the current sampling point and the previous sampling point are on the same side of the maximum power point, and no calculation is performed, proceeding to 4.3; if A is less than zero, it indicates that the maximum power point is between the current sampling point and the previous sampling point. In this case, the step size ratio parameter a in the arctangent step size function is reduced by half, and 4.3 is executed.

[0019] If the dp / dv obtained in step 3 is less than zero, it indicates that the maximum power point is to the left of the current point. Determine the sign of A. If A is greater than zero, it indicates that the current sampling point and the previous sampling point are on the same side of the maximum power point, and no calculation is performed before proceeding to 4.3. If A is less than zero, it indicates that the maximum power point is between the current sampling point and the previous sampling point. In this case, the step size ratio parameter a in the arctangent step size function is reduced by half, and 4.3 is executed.

[0020] If the dp / dv obtained in step three is equal to zero, stop the calculation and return to step two;

[0021] Step 4.3: Substitute the current dp / dv into equation (1) to calculate u(dp / dv), and substitute the temperature difference between the hot and cold ends of the thermoelectric element into equation (2) to obtain the temperature disturbance factor λ. i ;

[0022] If u(dp / dv) is greater than 0.95, it indicates that the operating point is far from the maximum power point, and the output step size d1 is used. If u(dp / dv) is not greater than 0.95, the comparison continues to see if u(dp / dv) is greater than 0.55. If it is greater than 0.55, the output step size d2 is used. If it is less than or equal to 0.55 and greater than 0, the output step size d3 is used.

[0023] If u(dp / dv) is less than -0.95, it indicates that the operating point is far from the maximum power point, and the output step size d1 is used. If u(dp / dv) is not less than -0.95, the comparison continues to see if u(dp / dv) is less than -0.55. If it is less than -0.55, the smaller step size d2 is output. If it is greater than or equal to -0.55 and less than 0, the smallest step size d3 is output.

[0024] Step 5: Adjust the duty cycle according to the step size obtained in Step 4 to achieve MPPT control.

[0025] The load matching method for temperature-based variable step size MPPT for combined heat and power (CHP) disclosed in this invention includes the following steps:

[0026] Step 1: After the fuel heater starts working, it discharges high-temperature fuel gas, and cooling water is introduced into the radiator;

[0027] Step 2: The high temperature of the gas transferred to the surface of the collector provides heat to the hot end of the thermoelectric element, while the cold end of the thermoelectric element is cooled by the radiator. The two ends of the thermoelectric element utilize the temperature difference to generate a potential difference and output electrical energy based on Seebeck's law of the thermoelectric element.

[0028] Step 3: After the potential difference generated by the thermoelectric element in Step 2 is connected to the control module, a DC-DC circuit is used as the basic circuit. The load is matched by changing the duty cycle of the switching transistor in the circuit to achieve the maximum power output.

[0029] Step 3.1: Real-time acquisition of the voltage and current of the thermoelectric element connected to the DC-DC circuit, and calculation of the power;

[0030] Step 3.2: Based on the voltage and current collected in Step 3.1, input them into the controller, and simultaneously collect the current temperature and the hot and cold ends temperature of the thermoelectric element to perform maximum power point tracking calculation;

[0031] Step 4: When the fuel oil heater starts working, the high-temperature gas discharged is fed into the collector of the combined heat and power unit. By using the maximum power point tracking method in step 3 to maximize the output power through the perturbation of the output voltage, the impedance matching of the load is achieved.

[0032] Beneficial effects:

[0033] 1. To address the issues of low output power and low output efficiency in thermoelectric power generation systems, this invention discloses a temperature-based variable step size MPPT method for thermoelectric cogeneration. After the thermoelectric power generation system outputs power, MPPT control is used to stabilize the output power of the thermoelectric power generation system near its maximum power point, thereby improving the output performance of the thermoelectric power generation system.

[0034] 2. The present invention discloses a temperature-based variable step size MPPT method for thermoelectric cogeneration. By introducing an arctangent step size function, the distance between the current operating point and the maximum power point is determined by substituting the power-voltage differential into the arctangent step size function and comparing it with relevant node values. This provides a basis for step size calculation, realizes piecewise variation of the step size, and improves the accuracy of MPPT control.

[0035] 3. The present invention discloses a temperature-based variable step size MPPT method for thermoelectric cogeneration, which collects the hot and cold end temperatures of the thermoelectric element, processes the hot end temperature and the temperature difference between the hot and cold ends through a calculation function and introduces a temperature perturbation factor to achieve the effect of real-time change of step size with temperature change, and realizes a wide range of rapid response of step size.

[0036] 4. The present invention discloses a temperature-based variable step size MPPT method for thermoelectric cogeneration, which achieves temperature-based step size output by combining multi-segment large-range adjustment of the disturbance step size with single-segment small adjustment. Combined with DC-DC circuit, the thermoelectric power generation system outputs electricity stably at its maximum power point, thereby improving the output performance of the thermoelectric power generation system. Attached Figure Description

[0037] Figure 1 This is a flowchart of a temperature-based variable step size MPPT method for thermoelectric cogeneration disclosed in this invention.

[0038] Figure 2 This is a graph of the arctangent step size function used in the temperature-based variable step size MPPT method for thermoelectric cogeneration disclosed in this invention.

[0039] Figure 3 This is a PV curve of a thermoelectric array. Specific implementation methods

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0041] Example 1:

[0042] like Figure 1 The flowchart shown in this embodiment illustrates a temperature-based variable-step MPPT method for thermoelectric combined heat and power (CHP). The specific implementation steps are as follows:

[0043] Step 1: Measure the output power and output voltage curves of the thermoelectric element, as shown in the figure below. Figure 3 As shown; a temperature difference is formed between the high-temperature gas and the cooling water at both ends of the thermoelectric element, generating a potential difference and outputting electrical energy.

[0044] Step 2: Collect the voltage and current of the electrical energy mentioned in Step 1, as well as the temperature of the hot and cold ends of the thermoelectric element;

[0045] Step 3: Based on the voltage and current collected in Step 2, calculate the power at this time, and subtract the power at this time from the power calculated at the previous moment to get dp. Subtract the voltage at this time from the voltage collected at the previous moment to get dv. Calculate dp / dv at this time, and multiply dp / dv at this time with dp / dv calculated at the previous moment to get A.

[0046] Step 4: Based on the curve from Step 1 and the sign of dp / dv at this point in Step 3, and in conjunction with... Figure 3 Calculate the step size;

[0047] Step 4.1: Introduce the arctangent step size function u(x), the graph of which is as follows: Figure 2 As shown, and the temperature disturbance factor λ i ;

[0048]

[0049] λ i =ε i (1+f(T h ,ΔT)) i=1,2,3 (2)

[0050]

[0051] d i =u(x)·λ i i = 1, 2, 3 (4)

[0052] Where a is the step size scaling parameter, x is the independent variable of the arctangent step size function, and ε i T is the step size factor. h T represents the hot end temperature of the thermoelectric element. hmax The maximum temperature that the hot end of the thermoelectric element can withstand is set to 400℃, and ΔT is the temperature difference between the hot and cold ends of the thermoelectric element. max The maximum temperature difference that the hot and cold ends of the thermoelectric element can withstand is set to 350℃.

[0053] Step 4.2: If the dp / dv obtained in Step 3 is greater than zero, it indicates that the maximum power point is to the right of the current point; determine the sign of A. When A is greater than zero, it indicates that the current sampling point and the previous sampling point are on the same side of the maximum power point, and no calculation is performed, proceeding to 4.3; if A is less than zero, it indicates that the maximum power point is between the current sampling point and the previous sampling point. At this time, the step size ratio parameter a in the arctangent step size function is reduced by half. The initial value of the step size ratio parameter a is 10, and 4.3 is executed.

[0054] If the dp / dv obtained in step 3 is less than zero, it indicates that the maximum power point is to the left of the current point. Determine the sign of A. If A is greater than zero, it indicates that the current sampling point and the previous sampling point are on the same side of the maximum power point, and no calculation is performed before proceeding to step 4.3. If A is less than zero, it indicates that the maximum power point is between the current sampling point and the previous sampling point. In this case, the step size ratio parameter a in the arctangent step size function is reduced by half. The initial value of the step size ratio parameter a is 10, and step 4.3 is executed.

[0055] If the dp / dv obtained in step three is equal to zero, stop the calculation and return to step two;

[0056] Step 4.3: Substitute the current dp / dv into equation (1) to calculate u(dp / dv), and substitute the temperature difference between the hot and cold ends of the thermoelectric element into equation (2) to obtain the temperature disturbance factor λ. i ;

[0057] If u(dp / dv) is greater than 0.95, it indicates that the operating point is far from the maximum power point, and the output step size d1 is 1×10. -3 ·u(dp / dv)·f(T h If u(dp / dv) is not greater than 0.95, then continue to compare whether u(dp / dv) is greater than 0.55. If it is greater than 0.55, then output the smaller step size d2 as 1×10. -4 ·u(dp / dv)·f(T h If ΔT is less than or equal to 0.55 and greater than 0, then the minimum output step size d3 is 1×10. -5 ·u(dp / dv)·f(T h ,ΔT);

[0058] If u(dp / dv) is less than -0.95, it indicates that the operating point is far from the maximum power point, and the output step size d1 is 1×10. -3 ·u(dp / dv)·f(T h If u(dp / dv) is not less than -0.95, then continue to compare whether u(dp / dv) is less than -0.55. If it is less than -0.55, then output the smaller step size d2 as 1×10. -4 ·u(dp / dv)·f(T h If ΔT is greater than or equal to -0.55 and less than 0, then the minimum output step size d3 is 1×10. -5 ·u(dp / dv)·f(T h ,ΔT);

[0059] Step 5: Adjust the duty cycle according to the step size obtained in Step 4 to achieve MPPT control.

[0060] The load matching method for temperature-based variable step size MPPT for combined heat and power (CHP) disclosed in this invention includes the following steps:

[0061] Step 1: After the fuel heater starts working, it discharges high-temperature fuel gas, and cooling water is introduced into the radiator;

[0062] Step 2: The high temperature of the gas transferred to the surface of the collector provides heat to the hot end of the thermoelectric element, while the cold end of the thermoelectric element is cooled by the radiator. The two ends of the thermoelectric element utilize the temperature difference to generate a potential difference and output electrical energy based on Seebeck's law of the thermoelectric element.

[0063] Step 3: After the potential difference generated by the thermoelectric element in Step 2 is connected to the control module, a DC-DC circuit is used as the basic circuit. The load is matched by changing the duty cycle of the switching transistor in the circuit to achieve the maximum power output.

[0064] Step 3.1: Real-time acquisition of the voltage and current of the thermoelectric element connected to the DC-DC circuit, and calculation of the power;

[0065] Step 3.2: Based on the voltage and current collected in Step 3.1, input them into the controller, and simultaneously collect the current temperature and the hot and cold ends temperature of the thermoelectric element to perform maximum power point tracking calculation;

[0066] Step 4: When the fuel oil heater starts working, the high-temperature gas discharged is fed into the collector of the combined heat and power unit. By using the maximum power point tracking method in step 3 to maximize the output power through the perturbation of the output voltage, the impedance matching of the load is achieved.

[0067] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A temperature-based variable-step MPPT method for thermoelectric cogeneration, characterized in that: Includes the following steps, Step 1: Measure the output power and output voltage curves of the thermoelectric element; a temperature difference is formed between the high-temperature gas and the cooling water at both ends of the thermoelectric element, generating a potential difference and outputting electrical energy. Step 2: Collect the voltage and current of the electrical energy mentioned in Step 1, as well as the temperature of the hot and cold ends of the thermoelectric element; Step 3: Based on the voltage and current collected in Step 2, calculate the power at this time, and subtract the power at this time from the power calculated at the previous moment to get dp. Subtract the voltage at this time from the voltage collected at the previous moment to get dv. Calculate dp / dv at this time, and multiply dp / dv at this time with dp / dv calculated at the previous moment to get A. Step 4: Calculate the step size based on the curve from Step 1 and the sign of dp / dv at this point in Step 3. Step four is implemented as follows: Step 4.1: Introduce the arctangent step size function u(x) and the temperature perturbation factor. ; （1） （2） （3） （4） in This is the step size scaling parameter. Let the arctangent step size function be the independent variable. Step size factor This refers to the hot end temperature of the thermoelectric element. To ensure the thermoelectric element's hot end can withstand the highest temperature, The temperature difference between the hot and cold ends of the thermoelectric element. To ensure the maximum temperature difference that the hot and cold ends of the thermoelectric element can withstand; Step 4.2: If the dp / dv obtained in Step 3 is greater than zero, it indicates that the maximum power point is to the right of the current point; determine the sign of A. When A is greater than zero, it indicates that the current sampling point and the previous sampling point are on the same side of the maximum power point, and no calculation is performed before proceeding to 4.

3. If A is less than zero, it indicates that the maximum power point is between the current sampling point and the previous sampling point. In this case, the step size ratio parameter a in the arctangent step size function is reduced by half, and 4.3 is executed. If the dp / dv obtained in step 3 is less than zero, it indicates that the maximum power point is to the left of the current point; determine the sign of A. When A is greater than zero, it indicates that the current sampling point and the previous sampling point are on the same side of the maximum power point, and no calculation is performed before proceeding to 4.

3. If A is less than zero, it indicates that the maximum power point is between the current sampling point and the previous sampling point. In this case, the step size ratio parameter a in the arctangent step size function is reduced by half, and 4.3 is executed. If the dp / dv obtained in step three is equal to zero, stop the calculation and return to step two; Step 4.3: Substitute the current dp / dv into equation (1) to calculate u(dp / dv), and substitute the temperature difference between the hot and cold ends of the thermoelectric element into equation (2) to obtain the temperature disturbance factor. ; If u(dp / dv) is greater than 0.95, it indicates that the operating point is far from the maximum power point, and the output step size is d1. If u(dp / dv) is not greater than 0.95, then continue to compare whether u(dp / dv) is greater than 0.

55. If it is greater than 0.55, then output a smaller step size d2. If the value is less than or equal to 0.55 and greater than 0, then output the minimum step size d3; If u(dp / dv) is less than -0.95, it indicates that the operating point is far from the maximum power point, and the output step size is d1. If u(dp / dv) is not less than -0.95, then continue to compare whether u(dp / dv) is less than -0.

55. If it is less than -0.55, then output the smaller step size d2. If the value is greater than or equal to -0.55 and less than 0, then output the minimum step size d3; Step 5: Adjust the duty cycle according to the step size obtained in Step 4 to achieve MPPT control.

2. The temperature-based variable step size MPPT method for thermoelectric cogeneration as described in claim 1, characterized in that: This system is based on a temperature difference combined heat and power (CHP) system, which includes a fuel oil heater, a CHP device, and a control module. The CHP device mainly consists of thermoelectric elements, a collector, and a radiator. During operation, fuel oil from the heater is discharged into the collector of the CHP device. The collector has a hollow interior and a flat outer surface. Thermoelectric elements are evenly distributed on the outer surface of the collector and are attached to the hot ends of the thermoelectric elements. A radiator is installed at the cold ends of the thermoelectric elements. The medium inside the radiator is replaced with cooling water. When a temperature difference is formed between the two ends of the thermoelectric elements, electrical energy is output. The output end is connected to the control module, which uses parameters such as external temperature to capture the maximum power point of the electrical energy output by the thermoelectric elements. The control module includes a DC-DC circuit and an MPPT controller. The DC-DC circuit mainly consists of diodes, switching transistors, inductors, and capacitors. The inductors and capacitors are used for energy storage and filtering, while the diodes are used for freewheeling. The MPPT controller, based on the collected voltage and current signals and combined with the output characteristics of the thermoelectric element, adjusts the output voltage by changing the duty cycle of the switching transistor, thereby achieving impedance matching for the load.

3. A method for load matching using the method described in claim 1, characterized in that: Includes the following steps, Step A: After the fuel heater starts working, it discharges high-temperature fuel gas, and cooling water is introduced into the radiator; Step B: The high temperature of the gas transferred to the surface of the collector provides heat to the hot end of the thermoelectric element, while the cold end of the thermoelectric element is cooled by the radiator. The two ends of the thermoelectric element utilize the temperature difference to generate a potential difference and output electrical energy based on Seebeck's law of the thermoelectric element. Step C: For the potential difference generated by the thermoelectric element in Step 2, after connecting it to the control module, a DC-DC circuit is used as the basic circuit. By changing the duty cycle of the switching transistor in the circuit, the load is matched to achieve the maximum power output. Step C1: Real-time acquisition of voltage and current when the thermoelectric element is connected to the DC-DC circuit, and calculation of power. Step C2: Based on the voltage and current collected in step C1, input them into the controller, and simultaneously collect the current temperature and the hot and cold ends temperature of the thermoelectric element, and perform maximum power point tracking calculation based on claim 1; Step D: When the fuel oil heater starts working, the high-temperature gas discharged is fed into the collector of the combined heat and power unit. By using the maximum power point tracking method in step three to maximize the output power through the perturbation of the output voltage, the impedance matching of the load is achieved.

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