A sampling-based frequency tracking control method for high-frequency induction heating power supplies

Abstract

This invention discloses a frequency tracking control method for a high-frequency induction heating power supply based on a sampling method, comprising: 1) setting the initial frequency of the induction heating power supply to f = f0 and starting the power supply; 2) setting the parameter Δx < 0; 3) using the power supply output square wave signal y as the trigger signal to trigger the CPU's AD sampling, acquiring the sine wave signal x, and obtaining the sampled value x1; directly identifying the frequency tracking control direction through the sign of the sampled value x1; 4) calculating the sampling deviation value Δx1 = x1 - Δx; realizing weak capacitive or weak inductive control of the power supply system by setting the value Δx; 5) sending the sampling deviation value Δx1 to a proportional-integral controller, and the integral controller outputs a frequency compensation signal Δf; 6) superimposing Δf with f, and updating the power supply frequency f = f + Δf in real time; 7) entering the next y control cycle and returning to step 2). This invention effectively solves the technical problems of existing digital frequency tracking control algorithms based on phase detection methods, such as complex structure, high CPU resource consumption, and cumbersome engineering implementation.

Description

Technical Field

[0001] This invention relates to a frequency tracking control method, and more particularly to a frequency tracking control method for a high-frequency induction heating power supply based on a sampling method. Background Technology

[0002] In high-frequency induction heating, the induction heating load is typically complex and time-varying during operation, leading to changes in the load resonant frequency. If the frequency of the induction heating power supply remains constant, on the one hand, the power switching devices of the induction heating power supply will be in a hard-switching state, increasing the voltage and current stress across the switches and increasing switching losses; on the other hand, it will increase the system's reactive power, reducing the heating power supply's efficiency and increasing output waveform ripple. Therefore, to enhance the operating efficiency and reliability of the induction heating power supply system, the system frequency must track the load resonant frequency, ensuring that the heating power supply always operates in a quasi-resonant state with a power factor close to 1, to adapt to changes in load parameters with temperature.

[0003] Currently, in the field of high-frequency induction heating, existing frequency tracking control technologies mainly fall into two categories: analog phase-locked loop (PLL) technology and digital phase-locked loop (PLL) technology.

[0004] 1) Analog phase-locked loop (PLL) technology mainly uses hybrid analog-digital PLL circuits based on the integrated PLL circuit CD4046, which has been widely used in practical engineering. The drawbacks of this method are its narrow frequency locking range and the inherent limitations of analog devices, such as temperature drift and poor anti-interference capabilities. When the load conditions are complex or the load resonant frequency varies significantly, phase-locking failure is likely.

[0005] 2) Digital phase-locked loop (PLL) technology is mainly based on digital PLL control technology such as DSP or FPGA. Compared with analog control technology, digital PLL control technology not only has advantages in stability, reliability, and anti-interference performance, but also has flexible design and fast processing speed.

[0006] Analysis of extensive literature reveals that existing frequency tracking control technologies based on digital phase-locked loops (PLLs) typically rely on phase detection. The basic principle is to detect the phase difference between the output voltage and current of the induction heating power supply in real time, and then use a PI regulator to control this phase difference to zero for real-time frequency tracking control. This method usually consists of several modules: ① voltage and current phase detection, ② voltage and current phase difference detection, ③ low-pass filtering, ④ phase difference sign recognition, ⑤ PI regulation, and ⑥ frequency control. Specifically: ① the voltage and current phase detection module primarily uses a zero-crossing comparator to convert the high-frequency sinusoidal voltage or current signal into a square wave signal; ② the voltage and current phase difference detection module mainly obtains the phase difference of the voltage and current square wave signals through an XOR or XNOR circuit; ③ the low-pass filter is mainly used to obtain the average value of the phase difference; ④ the phase difference sign recognition module is used to determine whether the voltage leads or lags the current, thereby determining the direction of frequency control; ⑤ the PI regulation is mainly used to control the phase difference to zero; and ⑥ the frequency control module is used to update the actual output frequency of the high-frequency induction heating power supply in real time. It is evident that, in such methods, whether it is the hybrid digital phase-locked loop technology based on DSP or the fully digital phase-locked loop technology based on FPGA, the shortcomings lie in the large number of frequency locking control links and the complexity of circuit or algorithm implementation. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a frequency tracking control method for high-frequency induction heating power supplies based on sampling method. This method can solve the technical problems of existing digital frequency tracking control algorithms based on phase detection method, such as complex structure, low stability, and cumbersome engineering implementation.

[0008] The objective of this invention is achieved as follows: a frequency tracking control method for a high-frequency induction heating power supply based on a sampling method, comprising the following steps:

[0009] Step 1) Set the initial frequency of the induction heating power supply to f = f0, and start the power supply.

[0010] Step 2) Set the parameter Δx < 0;

[0011] Step 3) Use the square wave signal y output by the power supply as the trigger signal to trigger the CPU's AD sampling, acquire the sine wave signal x, and obtain the sampled value x1; the direction of frequency tracking control is directly identified by the sign of the sampled value x1.

[0012] Step 4) Calculate the sampling deviation value Δx1 = x1 - Δx; use the set value Δx to achieve weak capacitive or weak inductive control of the power supply system;

[0013] Step 5) The sampling deviation value Δx1 is sent to the proportional-integral controller, and the integral controller outputs the frequency compensation signal Δf;

[0014] Step 6) Superimpose Δf and f to update the power supply frequency f = f + Δf in real time;

[0015] Step 7) Proceed to the next y control cycle and return to step 2).

[0016] As a further limitation of the present invention, the constant induction heating power supply mentioned in step 1) specifically includes a current-type inverter and a voltage-type inverter.

[0017] As a further limitation of the present invention, step 2) specifically includes: using a square wave y as the sampling signal and a sine wave signal x as the sampled signal, sampling the x signal once within one y cycle, and using the obtained sampled value x1 as a frequency tracking control variable.

[0018] As a further limitation of the present invention, when the induction heating power supply is a current-type inverter, the sine wave x is the power supply output voltage and the square wave y is the power supply output current; when the induction heating power supply is a voltage-type inverter, the sine wave x is the power supply output current and the square wave y is the power supply output voltage.

[0019] Compared with the prior art, the present invention adopts the above technical solution and has the following beneficial effects: 1) Saves control resources; The method of the present invention eliminates four control links, namely voltage and current phase detection, voltage and current phase difference detection, low-pass filter, and phase difference sign recognition, and replaces them with one data acquisition in each control cycle, which greatly reduces the complexity of the control algorithm, simplifies the hardware circuit design, saves digital CPU resources, and facilitates engineering implementation.

[0020] 2) Optimized frequency control direction identification; System frequency tracking direction control is a crucial technical step, referring to the direction of system frequency change in each control cycle, i.e., whether it increases or decreases. Existing technologies typically employ specialized control algorithms to determine whether voltage leads or lags current. This invention eliminates the need for additional control components, directly identifying the frequency tracking control direction from the sign of the sampled values, effectively reducing control complexity.

[0021] 3) Simplified system power factor control: To meet the soft-switching requirements of induction heating inverters and reduce system losses, the system is typically operated in a weak capacitive (current-source inverter) or weak inductive (voltage-source inverter) state. Existing technologies usually employ delay control algorithms, which delay the power supply output voltage (voltage-source inverter) or current (current-source inverter) before proceeding with other control processes. This invention directly superimposes a setpoint (corresponding to the control delay) onto the sampled values ​​to achieve voltage and current phase difference control, thereby meeting the power factor control requirements. Attached Figure Description

[0022] Figure 1 The control principle diagram of this invention.

[0023] Figure 2 The embodiment of the present invention is a current-type high-frequency induction heating power supply system.

[0024] Figure 3 System control flowchart in an embodiment of the present invention. Detailed Implementation

[0025] A frequency tracking control method for a high-frequency induction heating power supply based on sampling includes the following steps:

[0026] Step 1) Set the initial frequency of the induction heating power supply to f = f0, and start the power supply.

[0027] Step 2) Set the parameter Δx < 0;

[0028] Step 3) Use the square wave signal y output by the power supply as the trigger signal to trigger the CPU's AD sampling, acquire the sine wave signal x, and obtain the sampled value x1; the direction of frequency tracking control is directly identified by the sign of the sampled value x1.

[0029] Step 4) Calculate the sampling deviation value Δx1 = x1 - Δx; use the set value Δx to achieve weak capacitive or weak inductive control of the power supply system;

[0030] Step 5) The sampling deviation value Δx1 is sent to the proportional-integral controller, and the integral controller outputs the frequency compensation signal Δf;

[0031] Step 6) Superimpose Δf and f to update the power supply frequency f = f + Δf in real time;

[0032] Step 7) Proceed to the next y control cycle and return to step 2).

[0033] The method of this invention is applicable to both current-type and voltage-type high-frequency induction heating power supplies. For example... Figure 1 As shown, when the induction heating power supply is a current-source inverter, the sine wave x represents the power supply output voltage and the square wave y represents the power supply output current; when the induction heating power supply is a voltage-source inverter, the sine wave x represents the power supply output current and the square wave y represents the power supply output voltage. Using the square wave y as the sampling signal and the sine wave signal x as the sampled signal, the x signal is sampled once within one y cycle, and the obtained sampled value x1 is used as the frequency tracking control variable.

[0034] The power supply output frequency is accurately tracked by the load resonant frequency by controlling the sampled value x1 to zero or a certain set value Δx; the weak capacitive (current-source inverter) or weak inductive (voltage-source inverter) control of the power system is achieved by using the set value Δx, thereby realizing soft switching of the power supply; the direction of frequency tracking control is directly identified by the sign of the sampled value x1.

[0035] This paper uses a current-type parallel resonant high-frequency induction heating power supply as an example to illustrate the implementation of this invention patent:

[0036] Figure 2 This invention relates to a current-type parallel resonant high-frequency induction heating power supply based on the frequency tracking control method described in this invention. The main circuit consists of a three-phase thyristor rectifier, an H-bridge inverter, and a resonant load. On the grid side, a thyristor phase-controlled rectifier is used to regulate the power supply and a filter circuit composed of L0 and C0 smooths the DC output voltage. d This is a DC smoothing reactance, providing a constant current source for the H-bridge resonant inverter. The load side consists of C and L. r This forms an LC-type parallel resonant circuit, providing heating power for the heated steel strip.

[0037] (1) Signal conditioning: such as Figure 2 As shown, the output voltage u of the power inverter is detected in real time using voltage and current sensors. H and current i H Signal, and analog signal u H and i H Appropriate conditioning can be performed, such as filtering out high-frequency interference signals or harmonic components in analog signals, and performing appropriate linear transformations (amplification or reduction) on the signals.

[0038] (2) In this implementation case, the power supply capacity is set to 20kW; the main processor CPU uses the DSP chip TMS320F28035, and makes full use of the chip's enhanced capture eCAP module, analog-to-digital converter ADC, enhanced pulse width modulator ePWM, and timer0 and other internal peripherals to realize the relevant control functions. Among them: signal i H Connect to the eCAP1 port of the DSP chip and define rising edge triggering; u H The AD1 input port of the ADC module connected to the DSP chip.

[0039] (3) Control process as follows Figure 3 As shown, 1) CPU configuration and system initialization, DSP chip TMS320F28035 initialization and system control parameter initialization, setting the system initial frequency f0=100kHz, and controlling the delay voltage deviation Δu=-0.5A;

[0040] 2) When eCAP1 captures i H At the rising edge, the AD module is started to sample u. H And assign the sampled value to the variable u H1 ;

[0041] 3) Delay control, calculate the sampling deviation value Δu H1 =u H1 -Δu is used to implement weak capacitive control of the system;

[0042] 4) PI regulation control: ΔuH1 is sent to the proportional-integral PI regulator, and the PI regulator outputs the frequency compensation signal Δf.

[0043] 5) System frequency update control, f = f + Δf;

[0044] 6) PWM pulse generation. The ePWM period register and compare register are updated in real time according to the system frequency f to generate a PWM pulse with a 50% duty cycle, which triggers the H-bridge inverter to work.

[0045] This invention proposes a frequency tracking control method for high-frequency induction heating power supplies based on sampling, which effectively solves the technical problems of existing digital frequency tracking control algorithms based on phase detection, such as complex structure, high CPU resource consumption, and cumbersome engineering implementation.

[0046] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A frequency tracking control method for a high-frequency induction heating power supply based on sampling, characterized in that, Includes the following steps: Step 1) Set the initial frequency of the induction heating power supply to f=f0 and start the power supply; Step 2) Set parameter Δx < 0; use square wave y as the sampling signal and sine wave x as the sampled signal, sample the x signal once within one y cycle, and use the obtained sampled value x1 as the frequency tracking control variable; when the induction heating power supply is a current-type inverter, the sine wave x is the power supply output voltage and the square wave y is the power supply output current; when the induction heating power supply is a voltage-type inverter, the sine wave x is the power supply output current and the square wave y is the power supply output voltage. Step 3) Use the square wave signal y output by the power supply as the trigger signal to trigger the CPU's AD sampling, acquire the sine wave signal x, and obtain the sampled value x1; the direction of frequency tracking control is directly identified by the sign of the sampled value x1. Step 4) Calculate the sampling deviation value Δx1 = x1 - Δx; use the set value Δx to achieve weak capacitive or weak inductive control of the power supply system; Step 5) The sampling deviation value Δx1 is sent to the proportional-integral controller, and the integral controller outputs a frequency compensation signal. ; Step 6) Superimposed with f, the power supply frequency is updated in real time. ; Step 7) Proceed to the next y control cycle and return to step 2).

2. The high-frequency induction heating power supply frequency tracking control method based on sampling method according to claim 1, characterized in that, The constant induction heating power supply mentioned in step 1) specifically includes a current-source inverter and a voltage-source inverter.

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