Multi-channel alternating current temperature control system and control method thereof

Abstract

The invention discloses a multi-channel alternating current temperature control system and a control method thereof, and belongs to the technical field of alternating current power supply temperature control, and the multi-channel alternating current temperature control system comprises a temperature detection unit, a power supply processing unit, a zero-cross detection unit, a main control unit and a temperature control unit. Multi-channel alternating current temperature control can be achieved, switching noise is reduced, the change of the duty ratio is reflected to a driving signal in real time through an algorithm, the driving signal is evenly distributed on the whole control time axis, output of an alternating current power supply is even, energy injected by a control object is even, and therefore high-precision temperature control is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of AC power supply temperature control, and in particular to a multi-channel AC temperature control system and a control method thereof. Background Art

[0002] There are many temperature control systems at present, including DC temperature control systems and AC temperature control systems. In high-power and high-heating rate situations, DC temperature control requires a switching power supply. The higher the power, the more expensive it is. In addition, the conversion efficiency of the AC-DC converter is generally less than 90%, and there is a certain loss. Therefore, AC temperature control is generally used in high-power temperature control situations.

[0003] Since the frequency of AC power is generally 50Hz, which is relatively low, in order to accurately control the output of energy, the phase angle control method can be used to accurately control the conduction time in each half-wave cycle, but this control method will bring very large switching noise (the di / dt at the moment of conduction is very large). The switching noise problem caused by phase angle control can be effectively avoided by the conduction angle control method, but the conventional conduction angle control method will bring about the problem of large temperature fluctuation. Therefore, a multi-channel AC temperature control system and its control method are proposed. Summary of the invention

[0004] The technical problem to be solved by the present invention is: how to solve the noise problem caused by the existing phase angle control and the problem of large temperature fluctuation caused by the conduction angle control, and provides a multi-channel AC temperature control system.

[0005] The present invention solves the above technical problems through the following technical solutions. The present invention includes a temperature detection unit, a power processing unit, a zero-crossing detection unit, a main control unit and a temperature control unit;

[0006] The temperature detection unit is used to detect and obtain the temperature signal of each target temperature zone, convert the temperature signal into a voltage signal, and convert the voltage signal into a digital signal;

[0007] The power processing unit is used to convert the mains power into power supply for each target temperature zone;

[0008] The zero-crossing detection unit is used to detect the zero-crossing signal of the mains power;

[0009] The main control unit is used to obtain the digital signal in the temperature detection unit and convert it into a real-time temperature value, obtain the zero-crossing signal detected by the zero-crossing detection unit, perform switch control on the power processing unit, calculate the target setting duty cycle through the temperature control algorithm, and perform half-wave control and output according to the zero-crossing signal to obtain the temperature control signal of each target temperature zone;

[0010] The temperature control unit is used to convert the temperature control signal into a power control signal of the heating module in each target temperature zone, so as to realize the temperature control of each target temperature zone.

[0011] Furthermore, in the temperature detection unit, temperature detection is achieved by using a temperature sensor.

[0012] Furthermore, the temperature sensor is a platinum resistance temperature sensor, which is implemented by integrated chip sampling or by a temperature sampling circuit.

[0013] Furthermore, the power processing unit includes a transformer T1, a protection relay RLY1, a rectifier bridge U2, a resistor R3, a resistor R4 and a switch tube Q2, wherein the transformer T1 is used to step down the mains voltage, the protection relay RLY1 is used to perform switching control on the AC power output by the transformer T1, the rectifier bridge U2 performs full-wave rectification on the AC power output by the transformer T1, and the rectified power supply HPWR is a continuous half-wave, the resistor R3, the resistor R4 and the switch tube Q2 are used to drive the protection relay RLY1, the resistor R3 provides a base current for the switch tube Q2, and the resistor R4 is a pull-down resistor.

[0014] Furthermore, the switch tube Q2 is an NPN transistor or an NMOS tube.

[0015] Furthermore, in the zero-crossing detection unit, the zero-crossing signal is a signal at the moment when the voltage of the AC power supply is zero. At each moment when the voltage of the AC power supply is zero, a pulse is generated. The main control unit detects the pulse to determine when the voltage of the AC power supply is zero. By determining the moment when the voltage is zero, the power MOS tube Q1 in the temperature control unit is controlled to be turned on and off, so that the voltage of the power MOS tube Q1 at all switch control moments during the temperature control process is close to zero, and the switching noise generated by the system is minimized.

[0016] Furthermore, the temperature control unit includes a resistor R1, a driver U1, a resistor R2, a power MOS tube Q1, a freewheeling diode D1 and a connector J1, wherein one end of the resistor R1 is grounded and the other end is connected to the temperature control signal, the driver U1 is used to convert the TTL level of the temperature control signal into a gate drive level of the power MOS tube Q1, one end of R2 is connected to the output of the driver U1, and the other end is connected to the gate of the power MOS tube Q1, the freewheeling diode D1 is connected in parallel at both ends of the heating module, and the connector J1 is connected to the heating module.

[0017] The present invention also provides a control method for the multi-channel AC temperature control system, which realizes half-wave control and output according to the zero-crossing signal and the duty cycle, and includes the following steps:

[0018] S1: When the zero-crossing signal of each AC power source arrives, an external interrupt of a zero-crossing signal is generated;

[0019] S2: The variable name of the target duty ratio calculated by the PID control algorithm is recorded as duty, with a range of 0 to 1.0, indicating that the duty ratio is 0% to 100%;

[0020] S3: Define a duty cycle accumulation value variable s_sumDuty, whose data type is the same as the target duty cycle duty;

[0021] S4: In the interrupt function of each zero-crossing signal, the value of the target duty cycle duty is summed with the duty cycle accumulated value s_sumDuty, and then the relationship between s_sumDuty and 1 is judged. If it is greater than or equal to 1, the power MOS tube Q1 is driven to turn on and output the AC half-wave. If it is less than 1, Q1 is driven to turn off and stop outputting the AC half-wave.

[0022] Furthermore, in step S2, the specific process of the PID control algorithm calculating the target duty cycle is: the main control unit converts the digital signal in the temperature detection unit into a real-time temperature value Tc, the target setting value is Ts, the temperature error ΔT=Ts-Tc, the cumulative error ΔTsum is the sum of the temperature errors of each cycle, and the differential term Derr is the difference between the temperature errors of two consecutive cycles. Through the PID control algorithm: target duty cycle=P*(ΔT+I*ΔTsum+D*Derr), the target duty cycle is calculated, where P, I, and D are proportional control parameters, integral control parameters, and differential control parameters, respectively.

[0023] Compared with the prior art, the present invention has the following advantages: the multi-channel AC temperature control system can realize multi-channel AC temperature control, reduce switching noise, and reflect the change of duty cycle to the drive signal in real time through an algorithm, so that the drive signal is evenly distributed on the entire control time axis, the output of the AC power supply is uniform, and the energy injected into the control object is uniform, thereby realizing high-precision temperature control. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic structural diagram of a multi-channel AC temperature control system in an embodiment of the present invention;

[0025] Figure 2 is a circuit schematic diagram of a temperature control unit in an embodiment of the present invention;

[0026] Figure 3 is a circuit schematic diagram of a power processing unit in an embodiment of the present invention;

[0027] Figure 4 is a relationship diagram of an AC power supply, a zero-crossing signal and a zero-crossing interruption in an embodiment of the present invention;

[0028] Figure 5 is a flow chart of a temperature control algorithm in an embodiment of the present invention;

[0029] Figure 6 This is an example diagram of the actual control AC power output waveform in an embodiment of the present invention (the duty cycle is 0.228). DETAILED DESCRIPTION

[0030] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0031] like Figure 1 As shown, this embodiment provides a technical solution: a multi-channel AC temperature control system, including a main control unit, a temperature control unit, a temperature detection unit, a power processing unit and a zero-crossing detection unit;

[0032] The main control unit mainly uses the MCU to realize the output of temperature control signals, read the temperature signal of the temperature detection unit and convert it into a temperature value, control the switch of the power supply, and detect the zero-crossing signal. In addition to realizing the output of control signals and the detection of temperature signals, the main control unit also needs to implement the temperature control algorithm. Generally, the output duty cycle of the temperature control is obtained through the PID control algorithm, and then the half-wave control and output are performed through the conduction angle control algorithm, ultimately achieving the purpose of high-precision temperature control. (The temperature control algorithm is the general name for the temperature control achieved by the PID control algorithm and the conduction angle control algorithm together)

[0033] like Figure 2As shown, the temperature control unit converts the temperature control signal into the power control of the heating module. This unit includes a resistor R1, a driver U1, a resistor R2, a power MOS tube Q1, a freewheeling diode D1 and a connector J1. One end of the resistor R1 is grounded, and the other end is connected to the temperature control signal. When the MCU is powered on and the core is operating normally, the temperature control signal is ensured to be low level, so that the output remains in the closed state. The driver U1 realizes the conversion of the TTL level into the gate drive level of the power MOS tube Q1, increases the Vgs voltage of the power MOS tube Q1, reduces the on-resistance of the power MOS tube Q1, and improves the driving ability of the power MOS tube, thereby reducing the switching loss of the power MOS tube; it is required that the threshold value of the high level of the input signal of U1 shall not exceed the high level voltage value of the temperature control signal output by the MCU. One end of R2 is connected to the output of the driver U1, and the other end is connected to the gate of the MOS tube, which plays a role in protecting the gate of the MOS tube and matching the impedance. This resistor should not be too large, otherwise it will affect the switching speed of the power MOS tube Q1. The power MOS tube Q1 is a power device, and its heat dissipation capacity needs to be increased. When the load (heating module) has a large power, ensure that the continuous drain current Id of Q1 is more than twice the load current; at the same time, the drain-source voltage value Vds of Q1 needs to be greater than the maximum value of the half-wave voltage. Diode D1 is connected in parallel at both ends of the heating module as a freewheeling diode. When Q1 is turned off, it provides a freewheeling circuit for the load. J1 is a connector for connecting the heating module, and the connector is required to meet the overcurrent capacity of the rated working current of the heating module.

[0034] The temperature detection unit converts the temperature signal of the temperature sensor into a voltage signal, and converts the analog voltage signal into a digital signal. The main control unit reads and calculates the real-time temperature value at the temperature sensor. Under the requirement of high-precision temperature sampling, platinum resistance temperature sensors are generally selected. Their good linearity and wide temperature detection range can be applied to most scenarios. The detection of platinum resistance temperature sensors can be achieved through integrated chip sampling or high-precision temperature sampling circuits. It is recommended to use constant current drive and differential sampling.

[0035] like Figure 3 As shown, the power processing unit converts the mains electricity into the power supply for the target temperature zone. The unit mainly includes transformer T1, protection relay RLY1, rectifier bridge U2, resistor R3, resistor R4 and transistor Q2;

[0036] Because the temperature control system can select different target power supply voltages, the power frequency transformer T1 is used for conversion. At the same time, after isolation through the transformer, the heating circuit is safer and can effectively prevent electric shock. The transformer needs to pay attention to the output power to prevent the transformer saturation problem caused by excessive load power.

[0037] The protection relay RLY1 can control the switch of the AC power output by the transformer T1. When the AC zero-crossing signal is abnormal or the heating temperature is abnormal, the driving power enable signal is low, and the AC power is cut off to ensure the safety and reliability of the equipment. The rectifier bridge U2 performs full-wave rectification on the AC power output by the transformer T1, and the rectified power supply HPWR is a continuous half-wave. The rectifier bridge U2 can use an integrated chip or 4 diodes to realize the rectification function. Resistor R3, resistor R4, and transistor Q2 are used to drive the switch of the protection relay RLY1. Resistor R3 provides base current for transistor Q2, and resistor R4 is a pull-down resistor to ensure that transistor Q2 is always in the off state during the MCU startup process, so that the protection relay RLY1 is turned off; Q2 is an NPN transistor, which controls the switch of the protection relay RLY1 by controlling the conduction and cutoff of transistor Q2. Transistor Q2 can also be replaced by an NMOS tube.

[0038] The zero-crossing detection unit detects the zero-crossing signal of the mains, which is the signal when the AC power supply voltage is zero. At each moment when the AC power supply voltage is zero, a pulse is generated. The main control unit detects the pulse to determine when the AC power supply voltage is zero. By determining the moment when the voltage is zero, the power MOS tube Q1 in the temperature control unit is turned on and off to ensure that the voltage of the MOS tube is close to zero at all switch control moments during the temperature control process, so as to minimize the switching noise generated by the system.

[0039] Temperature control algorithm implementation:

[0040] At each zero-crossing signal arrival moment, an external interrupt of the zero-crossing signal is generated, and either the rising edge or the falling edge of the zero-crossing signal can be selected.

[0041] It is required to generate an external interrupt at the rising edge or falling edge of each zero-crossing signal. Each zero-crossing signal generates an interrupt, which is defined as a zero-crossing interrupt. In each interrupt function, the AC control algorithm of the present invention is called once to realize the driving control of the AC power supply.

[0042] Figure 4 , which shows the relationship between the AC power supply to be controlled, the detected zero-crossing signal, and the zero-crossing interruption generated when the zero-crossing signal arrives.

[0043] The main control unit converts the temperature signal of the temperature control unit into a real-time temperature value Tc. If the target setting value is Ts, the temperature error ΔT = Ts-Tc, the cumulative error ΔTsum is the sum of the temperature errors of each cycle, and the differential term Derr is the difference between the temperature errors of two consecutive cycles. The target duty cycle duty (real-time change) is obtained through the classic PID algorithm P*(ΔT+I*ΔTsum+D*Derr). The P, I, and D parameters need to be adjusted according to the control target. The PID algorithm also has a variety of variations, and you can flexibly choose the appropriate algorithm to match the actual application.

[0044] The target duty cycle calculated by the PID control algorithm is expressed in floating point type, the variable name is defined as duty, and the data range is 0 to 1.0, indicating a duty cycle of 0% to 100%;

[0045] Define a duty cycle accumulated value variable s_sumDuty, which needs to be a global variable or a static variable, and its data type is the same as that of the duty cycle duty.

[0046] The idea of ​​the temperature control algorithm is: in the interrupt function of each zero-crossing signal, the value of the target duty cycle duty is summed with the duty cycle accumulated value s_sumDuty, and then the relationship between s_sumDuty and 1 is judged. If it is greater than or equal to 1, Q1 is driven to turn on and output an AC half-wave. If it is less than 1, Q1 is driven to turn off and stop outputting the AC half-wave.

[0047] Figure 5 It is the flow chart of the algorithm, which briefly describes the idea of ​​the algorithm in a process way.

[0048] Here we use an example to demonstrate the final effect of the algorithm. Assuming that the target duty cycle is set to 0.228, we observe what kind of output waveform will be generated on the AC power supply. Figure 6 The waveform of the actual AC power output signal is described in.

[0049] Figure 6 The AC power output signal, the dotted line indicates that the AC power is not output, and the solid line indicates that the driver Q1 outputs the AC power.

[0050] Figure 6 The s_sumDuty represents the accumulated variable of the duty cycle. After each zero crossing, the latest duty is obtained and accumulated. When s_sumDuty is greater than or equal to 1, the drive output action is executed once, and an AC half-wave output is generated. At this time, s_sumDuty is reduced by 1, and so on. The final AC half-wave is evenly distributed on the entire time axis with an accurate duty cycle output.

[0051] In summary, the multi-channel AC temperature control system and the corresponding temperature control algorithm of the above-mentioned embodiment can realize multi-channel AC temperature control, reduce switching noise, and reflect the change of duty cycle to the drive signal in real time through the algorithm, so that the drive signal is evenly distributed on the entire control time axis, the output of the AC power supply is uniform, and the energy injected into the control object is uniform, thereby realizing high-precision temperature control.

[0052] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A multi-channel AC temperature control system, characterized in that: It includes a temperature detection unit, a power processing unit, a zero-crossing detection unit, a main control unit and a temperature control unit; The temperature detection unit is used to detect and obtain the temperature signal of each target temperature zone, convert the temperature signal into a voltage signal, and convert the voltage signal into a digital signal; The power processing unit is used to convert the mains power into power supply for each target temperature zone; The zero-crossing detection unit is used to detect the zero-crossing signal of the mains power; The main control unit is used to obtain the digital signal in the temperature detection unit and convert it into a real-time temperature value, obtain the zero-crossing signal detected by the zero-crossing detection unit, perform switch control on the power processing unit, calculate the target setting duty cycle through the temperature control algorithm, and perform half-wave control and output according to the zero-crossing signal to obtain the temperature control signal of each target temperature zone; The temperature control unit is used to convert the temperature control signal into a power control signal of the heating module in each target temperature zone, so as to realize the temperature control of each target temperature zone.

2. A multi-channel AC temperature control system according to claim 1, characterized in that: In the temperature detection unit, temperature detection is achieved by using a temperature sensor.

3. A multi-channel AC temperature control system according to claim 2, characterized in that: The temperature sensor uses a platinum resistance temperature sensor, which is implemented by integrated chip sampling or by a temperature sampling circuit.

4. A multi-channel AC temperature control system according to claim 1, characterized in that: The power processing unit includes a transformer T1, a protection relay RLY1, a rectifier bridge U2, a resistor R3, a resistor R4 and a switch tube Q2, wherein the transformer T1 is used to step down the mains voltage, the protection relay RLY1 is used to perform switch control on the AC power output by the transformer T1, the rectifier bridge U2 performs full-wave rectification on the AC power output by the transformer T1, and the rectified power supply HPWR is a continuous half-wave, the resistor R3, the resistor R4 and the switch tube Q2 are used to drive the protection relay RLY1, the resistor R3 provides a base current for the switch tube Q2, and the resistor R4 is a pull-down resistor.

5. A multi-channel AC temperature control system according to claim 4, characterized in that: The switch tube Q2 is an NPN transistor or an NMOS tube.

6. A multi-channel AC temperature control system according to claim 4, characterized in that: In the zero-crossing detection unit, the zero-crossing signal is a signal at the moment when the voltage of the AC power supply is zero. At each moment when the voltage of the AC power supply is zero, a pulse is generated. The main control unit detects the pulse to determine when the voltage of the AC power supply is zero. By determining the moment when the voltage is zero, the power MOS tube Q1 in the temperature control unit is controlled to be turned on and off, so that the voltage of the power MOS tube Q1 at all switch control moments during the temperature control process is close to zero, and the switching noise generated by the system is minimized.

7. A multi-channel AC temperature control system according to claim 6, characterized in that: The temperature control unit includes a resistor R1, a driver U1, a resistor R2, a power MOS tube Q1, a freewheeling diode D1 and a connector J1, wherein one end of the resistor R1 is grounded and the other end is connected to a temperature control signal, the driver U1 is used to convert the TTL level of the temperature control signal into a gate drive level of the power MOS tube Q1, one end of R2 is connected to the output of the driver U1, and the other end is connected to the gate of the power MOS tube Q1, the freewheeling diode D1 is connected in parallel at both ends of the heating module, and the connector J1 is connected to the heating module.

8. A control method for a multi-channel AC temperature control system according to claim 6 or 7, characterized in that: The half-wave control and output are realized according to the zero-crossing signal and the duty cycle, including the following steps: S1: When the zero-crossing signal of each AC power source arrives, an external interrupt of a zero-crossing signal is generated; S2: The variable name of the target duty ratio calculated by the PID control algorithm is recorded as duty, with a range of 0 to 1.0, indicating that the duty ratio is 0% to 100%; S3: Define a duty cycle accumulation value variable s_sumDuty, whose data type is the same as the target duty cycle duty; S4: In the interrupt function of each zero-crossing signal, the value of the target duty cycle duty is summed with the duty cycle accumulated value s_sumDuty, and then the relationship between s_sumDuty and 1 is judged. If it is greater than or equal to 1, the power MOS tube Q1 is driven to turn on and output the AC half-wave. If it is less than 1, Q1 is driven to turn off and stop outputting the AC half-wave.

9. The control method of a multi-channel AC temperature control system according to claim 7, characterized in that: In step S2, the specific process of the PID control algorithm calculating the target duty cycle is: the main control unit converts the digital signal in the temperature detection unit into a real-time temperature value Tc, the target setting value is Ts, the temperature error ΔT=Ts-Tc, the cumulative error ΔTsum is the sum of the temperature errors of each cycle, and the differential term Derr is the difference between the temperature errors of two consecutive cycles. Through the PID control algorithm: target duty cycle=P*(ΔT+I*ΔTsum+D*Derr), the target duty cycle is calculated, where P, I, and D are proportional control parameters, integral control parameters, and differential control parameters, respectively.

Images