A full-power energy-saving induction heating control method and device

Abstract

The present invention discloses a full-power energy-saving induction heating control method and device. The method includes: obtaining parameters of an electromagnetic induction heating system in real time; a three-phase PWM rectifier adopts double-closed-loop vector control to regulate the bus voltage; calculating the effective value of the load current through the actual value of the load current i L ; obtaining the effective value of the load current when the minimum bus voltage output by the PWM rectifier is constantly output to the half-bridge inverter circuit and the phase angle of the voltage and current output by the half-bridge inverter circuit I is 0 β ; according to I β0 * ; the electromagnetic induction heating system is segmented and controlled based on I β0 * , the bus voltage U dc and the effective value of the load current I , so that the PWM rectifier and the half-bridge inverter circuit operate in a constant voltage state and a phase modulation state respectively. The present invention can avoid overcurrent phenomenon in the starting state, greatly reduce the switching loss of the IGBT on the inverter side, and can effectively cope with the change of the internal resistance value of the inductor and the sudden increase and decrease of the inductor, and reduce the grid-side harmonics.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic induction heating, and particularly to a full-power energy-saving induction heating control method and device. Background Art

[0002] Compared with traditional heating means, electromagnetic induction heating technology has the characteristics of fast heating speed, high degree of automation, strong controllability, low loss, non-contact, and no pollution. With the development of power electronics technology, this technology has more flexible applications and experiences in the fields of medical treatment, furniture, chemical industry, and military industry. Compared with the full-bridge topology, the half-bridge topology can save a set of bridge arms, greatly saving costs, and has received wide attention and adoption from scholars and companies.

[0003] The half-bridge induction heating control method generally adopts the inductive control method, which has relatively high reliability and ensures low switching losses. The traditional method uses uncontrolled rectification or half-controlled rectification, which makes the bus voltage unable to be changed, restricting the improvement of the power level. On the other hand, due to the influence of the structure, the half-bridge inverter is relatively difficult to start oscillation. The existing inductive power control algorithm only considers turning on when the load current is zero, without considering the switching control under zero voltage conditions, resulting in more switching losses.

[0004] Therefore, there is an urgent need for a full-power energy-saving induction heating control algorithm to achieve energy-saving frequency conversion control with the highest efficiency. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide an energy-saving induction heating control method and device with full-power control to solve the above technical problems.

[0006] On the one hand, the present invention provides an energy-saving induction heating control method with full-power control, which is applicable to a three-phase PWM rectifier on the rectifier side and a half-bridge inverter circuit topology on the inverter side, and includes:

[0007] Obtaining the parameters of the electromagnetic induction heating system in real time, where the parameters include the bus voltage U dc , the actual value i of the load current L , the given value I0 of the load current, and the switching phase angle β of the half-bridge inverter circuit;

[0008] The three-phase PWM rectifier adopts double closed-loop vector control to regulate the bus voltage;

[0009] Calculating the effective value I of the load current through the actual value i of the load current L ;

[0010] Obtaining the effective value I of the load current when the minimum bus voltage output by the PWM rectifier is constantly output to the half-bridge inverter circuit and the phase angle β of the output voltage and current of the half-bridge inverter circuit is 0β0 * ;

[0011] According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the electromagnetic induction heating system is segmentedly controlled, so that the three-phase PWM rectifier and the half-bridge inverter circuit operate in a constant voltage state and a phase modulation state respectively; the constant voltage state means that the output voltage of the three-phase PWM rectifier follows the given value of the bus voltage in real time, and the effective value I of the load current is kept constant; the phase modulation state means that the on and off times of the half-bridge inverter circuit are controlled by the phase angle β to keep the effective value I of the load current constant.

[0012] Preferably, the electromagnetic induction heating system is segmentedly controlled according to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, and specifically includes:

[0013] The electromagnetic induction heating system is segmentedly controlled according to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, and the heating process is divided into low-power section heating and high-power section heating;

[0014] In the low-power section heating, the half-bridge inverter circuit operates in the phase modulation state, and the size of the effective value I of the load current is adjusted by controlling the phase angle β of the half-bridge inverter circuit switch;

[0015] In the high-power section heating, the three-phase PWM rectifier operates in the constant voltage state, and the size of the effective value I of the load current is controlled by controlling the bus voltage.

[0016] Preferably, the heating process is divided into low-power section heating and high-power section heating according to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, and specifically includes:

[0017] When the effective value I of the load current < (I β0 * - 50A), the bus voltage remains unchanged, and it is low-power section heating, where U s is the amplitude of the incoming line voltage;

[0018] When the effective value I of the load current > (I β0 * + 50A), it is high-power section heating;

[0019] Low-power heating and high-power heating can be quickly switched to achieve induction heating within the full power range; the implementation method for quickly switching between low-power heating and high-power heating is as follows:

[0020] When the switching phase angle β of the half-bridge inverter circuit approaches 0, the switching phase angle β of the half-bridge inverter circuit is quickly forced to 0 to achieve the quick switching between low-power heating and high-power heating.

[0021] Preferably, during low-power heating, the effective value I of the load current is adjusted by controlling the switching phase angle β of the half-bridge inverter circuit, which specifically includes:

[0022] Step 421: Control the rectifier-side bus voltage to be constant at U dc0 ;

[0023] Step 422: Start oscillation in the low-power section;

[0024] After the oscillation starts, calculate the switching phase angle β of the half-bridge inverter circuit;

[0025] Step 424: Adjust the load current amplitude according to the calculated switching phase angle β of the half-bridge inverter circuit.

[0026] Preferably, adjusting the load current amplitude according to the calculated switching phase angle β of the half-bridge inverter circuit specifically includes:

[0027] When the load current changes from negative to positive, switch S c1 turns on, and switch S c2 turns off; the rectifier-side power supply and capacitor C c1 supply power to the load simultaneously in two paths, which are S c1 -R-L-C c2 -S c1 and C c1 -S c1 -R-L-C c1 circuits;

[0028] After passing through a phase angle of π-β, switch S c1 turns off. Since the load is in a small inductive state, the load current forms an L-C c2 -D2-R-L circuit for freewheeling through diode D2; during the process of flowing through D2, the voltage drop across D2 is very small, and at this time, switch S c2 is turned on to achieve zero-voltage turn-on;

[0029] When the load current changes from positive to negative, since switch S c2 is already on and the inductor has discharged, the rectifier-side power supply and capacitor C c2 supply power to the load in the reverse direction simultaneously in two paths. One path is S c2 -Cc1 -L-R-S c2 One path is C c2 -L-R-S c2 -C c2 circuit;

[0030] After passing through a phase angle π-β, the switch S c2 turns off. Since the load is in a small inductive state, freewheeling occurs, forming an L-R-D1-C c1 -L freewheeling circuit; During the process of flowing through the diode D1, the switch S is turned on c1 ;

[0031] The above process is repeated in the subsequent cycles.

[0032] Preferably, for heating in the high power section, the effective value I of the load current is controlled by controlling the bus voltage, specifically including:

[0033] Step 431: Control the rectifier side bus voltage to be constant at U dc0 ;

[0034] Step 432: Start oscillation in the high power section;

[0035] Step 433: Calculate the bus voltage in real time;

[0036] Step 434: Adjust the amplitude of the load current by changing the bus voltage set value at the current moment in real time.

[0037] Preferably, the real-time calculation of the bus voltage is:

[0038]

[0039] where: U dc * (k) is the bus voltage set value at the current moment, ΔU dc is the voltage value to be changed, U dc * (k - 1) is the bus voltage set value at the previous moment;

[0040] The changed voltage value can be set as:

[0041]

[0042] where: k p 、k i are the proportional coefficient and integral coefficient, I0 is the load current set value, and I is the real-time effective value of the load current.

[0043] Preferably, the start-up oscillation in the low power section includes first turning on the switch S c1 , and turning off the switch S c2, causing the load current to appear the first upward trough. When the positive current becomes negative current, it enters the startup operation state;

[0044] Add a fixed delay time T1 during the switching interval between the upper and lower tubes; the time T1 is greater than the dead time and less than half of the resonant period time;

[0045] At the moment when the load current changes from positive to negative, switch S c1 disconnects, and after a delay of T1, switch S conducts again c2 ; when the load current changes from negative to positive, switch S disconnects c2 , and after a delay of T1, switch S conducts again c1 , and cycle for 8 ms in sequence to start the load.

[0046] Preferably, the startup of the high-power section includes first conducting switch S c1 , disconnecting switch S c2 , causing the load current to appear the first upward trough. When the positive current becomes negative current, it enters the startup operation state;

[0047] Add a fixed delay time T1 during the switching interval between the upper and lower tubes; the time T1 is greater than the dead time and less than half of the resonant period time;

[0048] At the moment when the load current changes from positive to negative, switch S c1 disconnects, and after a delay of T1, switch S conducts again c2 ; when the load current changes from negative to positive, switch S disconnects c2 , and after a delay of T1, switch S conducts again c1 , and cycle for 8 ms in sequence to start the load.

[0049] After the startup of the high-power section is completed, the delay time T1 is cleared to make the load current operate in resonance.

[0050] On the other hand, the present invention also provides an energy-saving induction heating control device with full-power control, which includes

[0051] a three-phase PWM rectifier, a half-bridge inverter circuit, a series resonant load, and a microcontroller. Among them, the induction coil of the series resonant load is the induction coil of the electric furnace, which is connected to the output end of the half-bridge inverter circuit and jointly bears the work of the resonant load with the bridge arm capacitor of the inverter;

[0052] The microcontroller includes an acquisition module, a double closed-loop vector control module, an effective value calculation module, an acquisition module, and a segmented control module;

[0053] The acquisition module is used to obtain the parameters of the electromagnetic induction heating system in real time. The parameters include the bus voltage U dc , the actual value of the load current i L, the given value of the load current I0 and the switching phase angle β of the half-bridge inverter circuit;

[0054] The double closed-loop vector control module is used for the double closed-loop vector control of the three-phase PWM rectifier to regulate the bus voltage;

[0055] The effective value calculation module is used to calculate the effective value I of the load current through the actual value i of the load current L ;

[0056] The acquisition module is used to acquire the effective value I of the load current when the minimum bus voltage output by the PWM rectifier is constantly output to the half-bridge inverter circuit and the phase angle β of the output voltage and current of the half-bridge inverter circuit is 0 β0 * ;

[0057] The segmented control module is used to segmentally control the electromagnetic induction heating system according to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, so that the three-phase PWM rectifier and the half-bridge inverter circuit operate in a constant voltage state and a phase modulation state respectively; the constant voltage state means that the output voltage of the three-phase PWM rectifier follows the given value of the bus voltage in real time to keep the effective value I of the load current constant; the phase modulation state means that the on and off times of the half-bridge inverter circuit are controlled by the phase angle β to keep the effective value I of the load current constant.

[0058] Compared with the prior art, the following technical effects are achieved:

[0059] The present invention proposes a new control strategy for a three-phase PWM rectifier and a half-bridge electromagnetic induction heating furnace system. This control method can not only expand the output power range, but also avoid overcurrent phenomenon during the startup state, greatly reducing the switching loss of the IGBT on the inverter side; it can effectively cope with the change of the internal resistance value of the inductor and the sudden increase and decrease of the inductor, and reduce the grid-side harmonics. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0061] Figure 1 is a flowchart of an energy-saving induction heating control method with full power control provided by an embodiment of the present invention;

[0062] Figure 2 is a current flow diagram for the present invention to control the phase angle β to adjust the amplitude of the load current.

[0063] Figure 3Block diagram of the low-power section heating control algorithm provided by an embodiment of the present invention.

[0064] Figure 4 Block diagram of the high-power section heating control algorithm provided by an embodiment of the present invention.

[0065] Figure 5 Structural schematic diagram of an energy-saving induction heating control device with full-power control provided by an embodiment of the present invention. Detailed implementation manners

[0066] The following details the implementation manners of the present invention. Examples of the implementation manners are shown in the accompanying drawings. The implementation manners described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as limiting the present invention.

[0067] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0068] The following details the optional embodiments of the present disclosure with reference to the accompanying drawings.

[0069] As Figure 1 shown, an energy-saving induction heating control method with full-power control adopts the following steps:

[0070] S100: Real-time obtain the parameters of the electromagnetic induction heating system, where the parameters include the bus voltage U dc , the actual value i of the load current L , the given value I0 of the load current, and the switching phase angle β of the half-bridge inverter circuit.

[0071] S200: The three-phase PWM rectifier adopts double closed-loop vector control to regulate the bus voltage.

[0072] Specifically, the PWM rectifier adopts a vector control strategy, that is, double closed-loop vector control. The double closed-loop refers to the voltage outer loop and the current inner loop.

[0073] Sample the three-phase incoming line voltage U adc and the incoming line current I abc as well as the bus voltage U dc . The three-phase incoming line voltage can obtain the grid vector angle θ through the phase-locked algorithm and is brought into the abc / dq and dq / ɑβ transformations. The three-phase incoming line current is transformed through coordinates to obtain the dq-axis current in the rotating coordinate system. Let the given value i of the q-axis current q * be 0. In addition, the real-time bus voltage U dc and the given value U dc* (t), the difference is passed through a PI regulator to obtain the d-axis current reference value i d * .

[0074] The dq-axis current values and the dq-axis current reference values are subtracted in real time, respectively passed through PI regulation to obtain the dq-axis voltage reference values, and the switching sequence is obtained through SVPWM to control the on / off of the switches (S rx (x = 1 to 6)) to achieve bus voltage regulation.

[0075] S300: Through the actual load current value i L Calculate to obtain the effective value I of the load current.

[0076] S400: Obtain the effective value I of the load current when the minimum bus voltage output by the PWM rectifier is constantly output to the half-bridge inverter circuit and the phase angle β of the output voltage and current of the half-bridge inverter circuit is 0 β0 * .

[0077] S500: According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the electromagnetic induction heating system is controlled in segments, so that the three-phase PWM rectifier and the half-bridge inverter circuit operate in a constant voltage state and a phase modulation state respectively; the constant voltage state means that the output voltage of the three-phase PWM rectifier follows the bus voltage reference value in real time to achieve a constant effective value I of the load current; the phase modulation state means that the on / off time of the half-bridge inverter circuit is controlled by the phase angle β to achieve a constant effective value I of the load current.

[0078] According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the electromagnetic induction heating system is controlled in segments, specifically including:

[0079] The heating process is divided into low-power section heating and high-power section heating according to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current;

[0080] In the low-power section heating, the half-bridge inverter circuit operates in the phase modulation state, and the size of the effective value I of the load current is adjusted by controlling the phase angle β of the half-bridge inverter circuit switch;

[0081] In the high-power section heating, the three-phase PWM rectifier operates in the constant voltage state, and the size of the effective value I of the load current is controlled by controlling the bus voltage.

[0082] In a possible implementation, according to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the heating process is divided into low-power section heating and high-power section heating, specifically including:

[0083] When the effective value I of the load current < (I β0 * - 50A), the bus voltage remains unchanged, for low-power section heating;

[0084] When the effective value I of the load current > (I β0 * + 50A), it is for high-power section heating;

[0085] The low-power section heating and high-power section heating can be quickly switched, so as to realize induction heating within the full power range.

[0086] Specifically, when the phase angle β of the bus voltage is forced to be 0, the recorded effective value of the tested load current is I β0 * . When the given value I of the load current < (I0 * - 50A), the bus voltage remains unchanged, for low-power section heating; when the given value I of the load current = (I β0 * ± 50A), at this time the bus voltage remains unchanged and β is forced to be 0; when I > (I β0 * + 50A), it is for high-power section heating. Thus, full-power power regulation is realized.

[0087] During low-power section heating, the half-bridge inverter circuit operates in the phase modulation state, and the effective value I of the load current is adjusted by controlling the phase angle β of the switches of the half-bridge inverter circuit, specifically including:

[0088] Step 421: Control the rectifier-side bus voltage to be constant at U dc0 ;

[0089] Step 422: Start oscillation in the low-power section;

[0090] In the embodiment of the present application, starting oscillation in the low-power section includes:

[0091] First turn on the switch S c1 , turn off the switch S c2 , so that the first trough of the load current appears. When the positive current becomes negative current, enter the oscillation running state;

[0092] Add a fixed delay time T1 during the switching interval between the upper and lower tubes; the time T1 is greater than the dead time and less than half of the resonant period time.

[0093] At the moment from positive to negative, switch S c1 Disconnects, delays for T1 and then conducts switch S c2 ; from negative to positive, disconnects switch S c2 , delays for T1 and then conducts switch S c1 , cycles for 8 ms in sequence to start the oscillation of the load.

[0094] Specifically, when the bus voltage reaches the initial given value U dc0 , first conducts switch S c1 , disconnects switch S c2 , so that the current appears the first valley. When the positive current becomes negative current, it enters the start-up operation state.

[0095] To ensure that there is no over-current phenomenon in the load current during start-up, add a start-up operation state, and the start-up operation time is 8 ms. Add a fixed delay time T1 during the switching interval between the upper and lower tubes. This time is greater than the dead time and less than half of the resonant period time. At the moment from positive to negative, switch S c1 Disconnects, delays for T1 and then conducts switch S c2 ; from negative to positive, disconnects switch S c2 , delays for T1 and then conducts switch S c1 , cycles for 8 ms in sequence, then the load can be started up and the load current can be reduced.

[0096] Step 423: After the start-up is completed, calculate the phase angle β of the switches in the half-bridge inverter circuit.

[0097] It should be noted that the phase angle β is related to the amplitude of the load current. For inductive power regulation, the larger the resonant frequency, the smaller the phase angle π-β, and the smaller the load current; the smaller the resonant frequency, the larger the phase angle π-β, and the larger the load current.

[0098] Specifically, sample the current to calculate the effective value I of the load current, subtract it from the given load current I0, and pass it through a PI regulator. Assume the variable output by the PI regulator is u out , the PI limit is u max , and the real-time resonant frequency is f. Then we can get:

[0099]

[0100] Among them, T(π-β) is the time corresponding to the phase angle π-β within half of the sine period, and the real-time resonant frequency f can be obtained by sampling the time difference of multiple current zero-crossing points.

[0101] Step 424: Adjust the amplitude of the load current according to the calculated phase angle β of the switches in the half-bridge inverter circuit.

[0102] Specifically, this method provides control over the phase angle β to adjust the amplitude of the load current. As Figure 2 shown, assume that a->b is the positive direction, and the black dashed line represents the direction of the load current.

[0103] When the load current changes from negative to positive, switch S c1 conducts, and switch S c2 turns off. The rectifier-side power supply and capacitor C c1 supply power to the load simultaneously through two paths, namely S c1 -R-L-C c2 -S c1 and C c1 -S c1 -R-L-C c1 circuits, as Figure 2 (a) shown;

[0104] After a phase angle of π-β, switch S c1 turns off. Since the load is in a small inductive state, the load current forms an L-C c2 -D2-R-L loop for freewheeling through diode D2, as Figure 2 (b) shown.

[0105] It should be noted that during the process of flowing through diode D2, the voltage drop across diode D2 is very small. At this time, turning on switch S c2 results in an on-loss that can be ignored. Therefore, after a dead time, switch S c2 turns on immediately to achieve zero-voltage turn-on.

[0106] When the load current changes from positive to negative, since switch S c2 is already conducting and the inductor has discharged, the rectifier-side power supply and capacitor C c2 supply power to the load in the reverse direction simultaneously through two paths. One path is S c2 -C c1 -L-R-S c2 , and the other path is C c2 -L-R-S c2 -C c2 circuits, as Figure 2 (c) shown;

[0107] After a phase angle of π-β, switch S c2 turns off. Due to the small inductive state of the load for freewheeling, an L-R-D1-C c1 -L freewheeling loop is formed, as Figure 2 (d) shown.

[0108] It should be noted that during the process of flowing through the diode D1, the voltage drop across the two ends of the diode D1 is very small. At this time, when S is turned on c1 , the turn-on loss caused is negligible. Therefore, after a dead time, the switch S c1 is immediately turned on.

[0109] The above process is repeated in the subsequent cycles, and the overall process is as shown in Figure 2 (e).

[0110] Substitute the phase angle β calculated in step 423 into step 424, and adjust the amplitude of the load current according to the calculated phase angle β of the switches in the half-bridge inverter circuit to complete the inductive power regulation.

[0111] It should be noted that for better understanding, the heating control in the low-power section in the embodiments of the present invention is further illustrated in the form of an algorithm block diagram, as shown in reference to Figure 3 . The purpose is to deepen the understanding of each implementation step of the method of the present invention.

[0112] During high-power heating, the three-phase PWM rectifier operates in a constant voltage state, and the effective value I of the load current is controlled by controlling the bus voltage, specifically including:

[0113] Step 431: Control the rectifier-side bus voltage to be constant at U dc0 .

[0114] Step 432: Start oscillation in the high-power section.

[0115] In the embodiments of the present application, starting oscillation includes:

[0116] First, turn on the switch S c1 , and turn off the switch S c2 , so that the first trough of the load current appears. When the positive current becomes negative current, enter the starting oscillation operation state;

[0117] Add a fixed delay time T1 during the switching interval between the upper and lower tubes; the time T1 is greater than the dead time and less than half of the resonant period time;

[0118] At the moment from positive to negative, the switch S c1 is turned off, and after a delay of T1, the switch S c2 is turned on; at the moment from negative to positive, the switch S c2 is turned off, and after a delay of T1, the switch S c1 is turned on, and this cycle repeats for 8 ms to start the oscillation of the load.

[0119] Specifically, when the bus voltage reaches the initial given value U dc0 , first turn on the switch S c1 , and turn off the switch S c2, causing the current to have its first upward trough. When the positive current becomes negative current, it enters the startup operation state;

[0120] To ensure that overcurrent does not occur in the load current during startup, a startup operation state is added, and the startup operation time is 8 ms. During the switching interval between the upper and lower tubes, a fixed delay time T1 is added. This time is greater than the dead time and less than half of the resonance period. At the moment from positive to negative, switch S c1 is turned off, and after a delay of T1, switch S c2 is turned on; at the moment from negative to positive, switch S c2 is turned off, and after a delay of T1, switch S c1 is turned on. By cycling in this way for 8 ms, the load can be started up and the load current can be reduced.

[0121] When the startup operation time ends, the delay time T1 is immediately cleared to 0. At the moment when the load current changes from positive to negative, switch S c1 is turned off, and switch S c2 is turned on; when the load current changes from negative to positive, switch S c1 is turned on, and switch S c2 is turned off. By cycling in this way, the load can be made to resonate.

[0122] It should be noted that the difference between startup in the high-power section and startup in the low-power section is that after startup in the high-power section, the delay T1 time is cleared to make the load current operate in resonance.

[0123] Step 433: Calculate the bus voltage in real time;

[0124] Based on the bus voltage, the effective value of the load-side current can be regulated, that is, the difference between the effective value of the current at each moment and the given value of the current effective value has a linear relationship with the bus voltage. The real-time calculation of the bus voltage is:

[0125]

[0126] In the formula: U dc * (t) is the given value of the bus voltage at the current moment t, ΔU dc is the voltage value that needs to change, and U dc * (t - 1) is the given value of the bus voltage at the previous moment.

[0127] The voltage value that changes can be set as:

[0128]

[0129] In the formula: k p and k i are the proportionality coefficient and the integral coefficient, I0 is the given value of the load current, and I is the real-time effective value of the load current.

[0130] It should be noted that when there is a difference between I and I0, the given value of the bus voltage changes, thereby reducing the difference between I and I0. Of course, the given value of the bus voltage is limited by overvoltage protection and cannot be too large or too small. It is preferably around 1.414 to 2 times the amplitude of the incoming line voltage.

[0131] Step 434: Adjust the amplitude of the load current by changing the given value of the bus voltage at the current moment in real time.

[0132] By continuously changing the given value of the bus voltage at the current moment, the peak value of the load current can be changed; the switching tubes on the inverter side only need to enter the normal operating state of Step 432, ensure that the switching action is carried out at the moment when the current passes through zero, and achieve the maximum reduction of switching losses and realize the energy-saving effect.

[0133] It should be noted that for better understanding, the high-power section heating control in the embodiments of the present invention is further described in the form of an algorithm block diagram, as shown in Figure 4 shown. The purpose is to deepen the understanding of each implementation step of the method of the present invention.

[0134] The above-mentioned low-power section heating and high-power section heating need to be switched and controlled, and it is required that the two methods can be switched arbitrarily without affecting the normal operation of the system.

[0135] Furthermore, the implementation method for the rapid switching between the low-power section heating and the high-power section heating is as follows:

[0136] When the switching phase angle β of the half-bridge inverter circuit approaches 0, the switching phase angle β of the half-bridge inverter circuit is forced to 0 quickly to realize the rapid switching between the low-power section heating and the high-power section heating.

[0137] Specifically, conduct an experiment, make the phase angle β of the bus voltage forced to 0, and record the measured effective value of the load current as I β0 * .

[0138] When the effective value of the load current I < (I β0 * - 50A), the bus voltage remains unchanged, and the method of inductive phase modulation and power regulation is used to control the effective value of the load current I; when the effective value of the load current I = (I β0 * ± 50A), at this time the bus voltage remains unchanged and β is forced to 0; when I > (I β0 * + 50A), the bus voltage power regulation method is adopted. Thus, full-power power regulation is realized.

[0139] Refer to Figure 5As shown in the figure, an energy-saving induction heating control device with full power control according to an exemplary embodiment of the present invention includes a three-phase PWM rectifier 1, a half-bridge inverter circuit 2, a microcontroller 3, and a series resonant load 4. Among them, the induction coil of the series resonant load is the induction coil of the electric furnace, which is connected to the output end of the half-bridge inverter circuit and jointly undertakes the work of the resonant load with the bridge arm capacitor of the inverter.

[0140] Specifically, the rectifier is a three-phase PWM rectifier bridge, which consists of six switching tubes S cx (x = 1 to 6), and a group of filter capacitors C d and can realize the functions of active power correction and bus voltage control; the half-bridge inverter circuit includes two bridge arms, one of which includes two switching tubes S c1 and S c2 , and the switching tubes are equipped with built-in diodes D1 and D2. The other bridge arm consists of two capacitors C c1 and C c2 . The output ends of the two bridge arms are connected to the load resistor R and the induction coil L.

[0141] The electromagnetic induction heating device with the above topology can be implemented and applied based on the control platform of DSP28377d.

[0142] The microcontroller includes an acquisition module, a double closed-loop vector control module, an effective value calculation module, an acquisition module, and a segmented control module;

[0143] The acquisition module is used to obtain the parameters of the electromagnetic induction heating system in real time. The parameters include the bus voltage U dc , the actual value of the load current i L , the given value of the load current I0, and the switching phase angle β of the half-bridge inverter circuit;

[0144] The double closed-loop vector control module is used for the double closed-loop vector control of the three-phase PWM rectifier to regulate the bus voltage;

[0145] The effective value calculation module is used to calculate the effective value I of the load current through the actual value i L of the load current;

[0146] The acquisition module is used to obtain the effective value I β0 * of the load current when the minimum bus voltage output by the PWM rectifier is constantly output to the half-bridge inverter circuit and the phase angle β of the output voltage and current of the half-bridge inverter circuit is 0;

[0147] The segmented control module is used to segment according to the effective value I β0 * of the load current and the bus voltage U dcBased on the effective value I of the load current, the electromagnetic induction heating system is segmented and controlled, enabling the three-phase PWM rectifier and the half-bridge inverter circuit to operate in a constant voltage state and a phase modulation state respectively. The constant voltage state means that the output voltage of the three-phase PWM rectifier follows the given value of the bus voltage in real time, achieving a constant effective value I of the load current. The phase modulation state means that by controlling the on and off times of the half-bridge inverter circuit through the phase angle β, a constant effective value I of the load current is achieved.

[0148] Furthermore, the segmented control module includes a low-power heating module and a high-power heating module.

[0149] The low-power heating module is used for heating in the low-power section. The half-bridge inverter circuit operates in the phase modulation state, and the magnitude of the effective value I of the load current is adjusted by controlling the phase angle β of the switches of the half-bridge inverter circuit.

[0150] The high-power heating module is used for the three-phase PWM rectifier to operate in the constant voltage state, and the magnitude of the effective value I of the load current is controlled by controlling the bus voltage.

[0151] Furthermore, when the effective value I of the load current < (I β0 * - 50A), the bus voltage remains unchanged for low-power section heating; when the effective value I of the load current > (I β0 * + 50A), it is for high-power section heating. The low-power section heating and the high-power section heating can be quickly switched, thus realizing induction heating within the full power range. The specific switching method is as follows: when the phase angle β of the switches of the half-bridge inverter circuit is close to 0, the phase angle β of the switches of the half-bridge inverter circuit is forced to 0 quickly to achieve the quick switching between the low-power section heating and the high-power section heating.

[0152] The present invention realizes inductive phase modulation power control in the low-power section to achieve zero-voltage switching; realizes voltage regulation resonance control in the high-power section to achieve zero-current switching and operate with maximum efficiency. By adopting a switching algorithm, the two control modes are switched steplessly to achieve energy-saving frequency conversion control with maximum efficiency.

[0153] It should be noted that the above description is only the specific implementation manner of the present invention. Those skilled in the art can clearly understand that for the sake of convenience and brevity of description, the specific working processes of the above-described system, module, and unit can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. An energy-saving induction heating control method with full power control, which is applicable to a three-phase PWM rectifier on the rectifier side and a half-bridge inverter circuit topology on the inverter side, and is characterized in that: Obtain the parameters of the electromagnetic induction heating system in real time, where the parameters include the bus voltage U dc , the actual value i of the load current L , the given value I0 of the load current, and the switching phase angle β of the half-bridge inverter circuit; The three-phase PWM rectifier adopts double closed-loop vector control to regulate the bus voltage; Based on the actual value i of the load current L the effective value I of the load current is calculated; Obtain the effective value I of the load current when the minimum bus voltage output by the PWM rectifier is constantly output to the half-bridge inverter circuit and the phase angle β of the output voltage and current of the half-bridge inverter circuit is 0 β0 * ; According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the electromagnetic induction heating system is segmented and controlled, so that the three-phase PWM rectifier and the half-bridge inverter circuit operate in a constant voltage state and a phase modulation state respectively; the constant voltage state means that the output voltage of the three-phase PWM rectifier follows the given value of the bus voltage in real time, and the effective value I of the load current is kept constant; the phase modulation state means that the on and off times of the half-bridge inverter circuit are controlled by the phase angle β to keep the effective value I of the load current constant; According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the electromagnetic induction heating system is segmented and controlled, specifically including: According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the heating process is divided into low-power heating and high-power heating; During heating in the low-power section, the half-bridge inverter circuit operates in the phase modulation state, and the effective value I of the load current is adjusted by controlling the phase angle β of the switches in the half-bridge inverter circuit; During heating in the high-power section, the three-phase PWM rectifier operates in the constant voltage state, and the effective value I of the load current is controlled by controlling the bus voltage.

2. The energy-saving induction heating control method with full power control according to claim 1, characterized in that: According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the heating process is divided into low-power heating and high-power heating, specifically including: When the effective value of the load current I < (I β0 * - 50 A), the bus voltage remains unchanged and heats in the low - power section, where U s is the amplitude of the incoming line voltage; When the effective value of the load current I > (I β0 * + 50 A), it is in the high-power section for heating; Heating in the low-power section and heating in the high-power section can be quickly switched, so as to realize induction heating within the full power range; the implementation method for quickly switching between heating in the low-power section and heating in the high-power section is: When the phase angle β of the switches in the half-bridge inverter circuit approaches 0, the phase angle β of the switches in the half-bridge inverter circuit is forced to be 0 quickly to realize the quick switching between heating in the low-power section and heating in the high-power section.

3. The energy-saving induction heating control method with full power control according to claim 2, characterized in that: During the heating in the low-power section, the effective value I of the load current is adjusted by controlling the phase angle β of the switches in the half-bridge inverter circuit, which specifically includes: Step 421: Control the rectifier side bus voltage to be constant at the given bus voltage U dc0 ; Step 422: Start oscillation in the low-power section; Step 423: After the oscillation starts, calculate the phase angle β of the switches in the half-bridge inverter circuit; Step 424: Adjust the amplitude of the load current according to the calculated phase angle β of the switches in the half-bridge inverter circuit.

4. The energy-saving induction heating control method with full power control according to claim 3, characterized in that: The adjustment of the amplitude of the load current according to the calculated phase angle β of the switches in the half-bridge inverter circuit specifically includes: When the load current changes from negative to positive, switch S c1 conducts, and switch S c2 turns off; the rectifier-side power supply and capacitor C c1 supply power to the load simultaneously in two paths, namely S c1 -R-L-C c2 -S c1 and C c1 -S c1 -R-L-C c1 circuits; After a phase angle of π-β, switch S c1 turns off. Since the load is in a slightly inductive state, the load current forms an L-C c2 -D2-R-L loop freewheeling through diode D2; during the process of flowing through D2, the voltage drop across D2 is very small, and at this time, switch S c2 is turned on; When the load current changes from positive to negative, since the switch S c2 has been turned on and the inductor has finished discharging, the rectifier-side power supply and the capacitor C c2 supply power to the load in the reverse direction simultaneously through two paths. One path is S c2 -C c1 -L-R-S c2 , and the other path is C c2 -L-R-S c2 -C c2 loop; After a phase angle of π-β, switch S c2 turns off. Since the load is in a slightly inductive state, freewheeling occurs, forming an L-R-D1-C c1 -L freewheeling loop; during the process of flowing through diode D1, switch S c1 is turned on; Repeat the above process in the subsequent cycles.

5. The energy-saving induction heating control method with full power control according to claim 2, characterized in that: During the heating in the high-power section, the effective value I of the load current is controlled by controlling the bus voltage, which specifically includes: Step 431: Control the rectifier side bus voltage to be constantly at U dc0 ; Step 432: Start oscillation in the high-power section; Step 433: Calculate the bus voltage in real time; Step 434: Adjust the amplitude of the load current by changing the given value of the bus voltage at the current moment in real time.

6. The energy-saving induction heating control method with full power control according to claim 5, characterized in that: The real-time calculation of the bus voltage is: Where: U dc * (k) is the given value of the bus voltage at the current moment, ΔU dc is the voltage value that needs to change, U dc * (k - 1) is the given value of the bus voltage at the previous moment; The set value of the changing voltage is: Where: k p , k i are the proportional coefficient and the integral coefficient, I0 is the given value of the load current, and I is the real-time effective value of the load current.

7. The energy-saving induction heating control method with full power control according to claim 3, characterized in that: The start oscillation in the low-power section includes Pilot turn-on switch S c1 , turn off switch S c2 , so that the load current appears the first upward trough. When the positive current becomes negative current, enter the start-up operation state; Adding a fixed delay time T1 during the switching interval between the upper and lower switches; the time T1 is greater than the dead time and less than half of the resonant period time; When the load current changes from positive to negative, switch S c1 turns off, and after a delay of T1, switch S turns on again c2 ; when it changes from negative to positive, switch S turns off c2 , and after a delay of T1, switch S turns on again c1 , and this cycle repeats every 8 ms to start the oscillation of the load.

8. The energy-saving induction heating control method with full power control according to claim 5, characterized in that: The start oscillation in the high-power section includes Pilot turn-on switch S c1 , turn off switch S c2 , so that the load current appears the first upward trough. When the positive current becomes negative current, enter the starting and oscillating operation state; Adding a fixed delay time T1 during the switching interval between the upper and lower switches; the time T1 is greater than the dead time and less than half of the resonant period time; At the moment when the load current changes from positive to negative, switch S c1 is turned off, and after a delay of T1, switch S is turned on again c2 ; when it changes from negative to positive, switch S is turned off c2 , and after a delay of T1, switch S is turned on again c1 , and this cycle repeats for 8 ms to start the oscillation of the load; After the start oscillation in the high-power section, the delay time T1 is cleared to make the load current operate in resonance.

9. An energy-saving induction heating control device with full power control, characterized in that: Includes A three-phase PWM rectifier, a half-bridge inverter circuit, a series resonant load and a microcontroller. Among them, the induction coil of the series resonant load is the induction coil of the electric furnace, which is connected to the output end of the half-bridge inverter circuit and jointly bears the work of the resonant load with the bridge arm capacitor of the inverter; The microcontroller includes an acquisition module, a double closed-loop vector control module, an effective value calculation module, an acquisition module and a segmented control module; The acquisition module is used to obtain the parameters of the electromagnetic induction heating system in real time, and the parameters include the bus voltage U dc , the actual value i of the load current L , the given value I0 of the load current, and the switching phase angle β of the half-bridge inverter circuit; The double closed-loop vector control module is used for the double closed-loop vector control of the three-phase PWM rectifier to regulate the bus voltage; The effective value calculation module is used to calculate the effective value I of the load current through the actual value i of the load current L ; The obtaining module is configured to obtain the effective value I of the load current when the minimum bus voltage output by the PWM rectifier is constantly output to the half-bridge inverter circuit and the phase angle β of the output voltage and current of the half-bridge inverter circuit is 0. β0 * ; The segmented control module is used to segmentally control the electromagnetic induction heating system according to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, so that the three-phase PWM rectifier and the half-bridge inverter circuit operate in a constant voltage state and a phase modulation state respectively; the constant voltage state means that the output voltage of the three-phase PWM rectifier follows the given value of the bus voltage in real time to keep the effective value I of the load current constant; the phase modulation state means that the on and off times of the half-bridge inverter circuit are controlled by the phase angle β to keep the effective value I of the load current constant; According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the electromagnetic induction heating system is segmented and controlled, specifically including: According to the effective value I of the load current β0 * , the bus voltage U dc and the effective value I of the load current, the heating process is divided into low-power heating and high-power heating; During heating in the low-power section, the half-bridge inverter circuit operates in the phase modulation state, and the effective value I of the load current is adjusted by controlling the phase angle β of the switches in the half-bridge inverter circuit; During heating in the high-power section, the three-phase PWM rectifier operates in the constant voltage state, and the effective value I of the load current is controlled by controlling the bus voltage.

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