A current zero-crossing detection apparatus and method for a half-bridge series resonant topology

Abstract

This invention proposes a current zero-crossing detection device and method for a half-bridge series resonant topology, belonging to the field of DC-AC inverter technology. The device includes: a voltage sampling circuit connected across a resonant capacitor in the half-bridge converter circuit; the sampling output of the voltage sampling circuit is divided into two sampling output signals with the same phase and amplitude; one sampling output signal is connected to the input of a phase-shifting circuit, and the other sampling output is connected to one input of a comparator circuit; the output of the phase-shifting circuit is connected to the other input of the comparator circuit; the comparator circuit generates a pulse output based on the signals from the two inputs to control the switching elements of the half-bridge converter circuit to turn on or off. Using the scheme of this invention, the leading phase-shifting circuit outputs a hardware switching control signal before the capacitor voltage reaches its peak point, allowing the half-bridge inverter system to effectively control the switching elements in a closed-loop manner using this switching control signal.

Description

Technical Field

[0001] This invention belongs to the field of DC-AC inverter technology, and particularly relates to a current zero-crossing detection device and method for a half-bridge series resonant topology. Background Technology

[0002] Currently, the mainstream topology for commercial induction cooker induction heating controllers in the 8-25kW power range is the half-bridge series resonant topology. In actual operation, the half-bridge series resonant inverter operates in the inductive load region to ensure its safety. If it enters the capacitive load region, a very high current spike will appear on the power transistor, and the heavier the load, the more obvious the spike will be.

[0003] To ensure that the inverter operates in an inductive state, the inverter sweeps the frequency from high to low when it starts working. When the load operating frequency reaches a value that is close to and slightly greater than the load resonant frequency, a phase-locked loop control is used to lock the frequency, so that the load operating frequency automatically tracks the load resonant frequency.

[0004] To ensure that the load operating frequency reaches a point close to and slightly above the load resonant frequency, the conventional approach is to use current transformers or current sensors on the coil to detect the zero-crossing point of the coil current. The power transistor is then turned off a certain amount of time before the inductor current reaches its zero-crossing point, thus ensuring that the load operating frequency reaches a point close to and slightly above the load resonant frequency.

[0005] Using components such as current transformers and current sensors increases costs. Furthermore, the internal core parameters of these components change under high-temperature conditions, requiring compensation. Some sensors also require additional power supply modules, and signal distortion may occur in high-frequency applications. Summary of the Invention

[0006] To address the aforementioned technical problems, a first aspect of the present invention provides a current zero-crossing detection device for a half-bridge series resonant topology. The device includes: a voltage sampling circuit connected across a resonant capacitor in a half-bridge converter circuit; the sampling output of the voltage sampling circuit is divided into two sampling output signals with the same phase and amplitude; one sampling output signal is connected to the input terminal of a phase-shifting circuit, and the other sampling output signal is connected to one input terminal of a comparator circuit; the output terminal of the phase-shifting circuit is connected to the other input terminal of the comparator circuit; the comparator circuit generates a pulse output based on the signals from the two input terminals to control the switching elements of the half-bridge converter circuit to turn on or off.

[0007] As described in the first aspect of the invention, the voltage sampling circuit is used to acquire a sinusoidal voltage signal across the resonant capacitor, and the phase shifting circuit shifts the sinusoidal voltage signal ahead of its phase by a predetermined angle.

[0008] As described in the first aspect of the invention, the phase-shifting circuit is an RC sine wave phase-shifting circuit, and the comparison circuit is a two-input comparator.

[0009] As described in the first aspect of the invention, the voltage sampling circuit uses an analog-to-digital converter to sample and convert the voltage across the resonant capacitor; the digital sampling signal output by the voltage sampling circuit is input to a microcontroller, and the microcontroller has built-in circuit modules that form a phase-shifting circuit module and a comparison circuit module to perform phase shifting and comparison on the digital sampling signal to generate the pulse output.

[0010] In the apparatus described in the first aspect of the invention, the voltage sampling circuit is integrated within the microcontroller.

[0011] As described in the first aspect of the present invention, the voltage sampling circuit, phase shifting circuit, and comparison circuit are all built into the microprocessor. The voltage sampling and analog-to-digital conversion module, the phase shifting circuit module, and the comparison circuit module are constructed by the software built into the microprocessor. Under the software control inside the microprocessor, the voltage across the resonant capacitor is sampled, the sampled output signal is phase shifted, and the sampled output signal and the phase-shifted sampled output signal are compared to generate a pulse output.

[0012] A second aspect of the present invention provides a current zero-crossing detection method for a half-bridge series resonant topology, for operating the aforementioned current zero-crossing detection circuit, the method comprising the following steps:

[0013] Step 1: The voltage sampling circuit connected to the two ends of a resonant capacitor in the half-bridge converter circuit detects the sinusoidal voltage across the resonant capacitor and generates two sampling output signals with the same phase and amplitude based on the sinusoidal voltage.

[0014] Step 2: One of the two sampled output signals generated in Step 1 is phase-shifted by a predetermined phase using a phase-shifting circuit to generate a phase-shifted sampled output signal; and the phase-shifted sampled output signal is input to one input of the comparator circuit.

[0015] The other sampling output of the two sampling output signals generated in step 1 is directly connected to the other input of the comparator circuit.

[0016] Step 3: The comparison circuit compares the two input signals and generates a pulse output to control the switching elements of the half-bridge converter circuit to turn on or off.

[0017] As described in the second aspect of the present invention, the phase shifting predetermined phase in step 2 includes obtaining the peak point of the voltage across the resonant capacitor, and using the peak point as a reference, shifting the sinusoidal voltage ahead of the peak point of the voltage across the resonant capacitor by an angle ψ through a phase shifting circuit.

[0018] As described in the second aspect of the present invention, step 3 further includes: generating the rising edge and falling edge of the pulse output at the starting point of the leading ψ angle described in step 2.

[0019] As described in the second aspect of the present invention, when the amplitude of the phase-shifted sampled output signal increases, a rising edge of the pulse output is generated, and when the amplitude of the phase-shifted sampled output signal decreases, a falling edge of the pulse output is generated.

[0020] In the scheme of this invention, the function of the advance phase shifting circuit is to output a hardware switch control signal before the capacitor voltage reaches its peak point (which is also the zero-crossing point of the inductor current). The half-bridge inverter system can use this switch control signal to perform effective closed-loop control of the switching elements. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a pre-existing half-bridge series resonant topology;

[0022] Figure 2 The voltage and current state diagram of a load operating in an inductive state in a half-bridge series resonant topology of existing technology.

[0023] Figure 3 This is a block diagram of the capacitor voltage lead phase shift circuit of the present invention;

[0024] Figure 4 This is a schematic diagram illustrating the logical relationship between the lead-shift voltage and the sampling capacitor voltage of the present invention;

[0025] Figure 5 This is the basic network schematic diagram of RC lead-shift phase shifting;

[0026] Figure 6 This is a schematic diagram showing the current direction before and after the current crosses zero when the upper transistor is conducting.

[0027] Figure 7 It is simplified. Figure 6 Current direction diagram.

[0028] Where C0 is the bus capacitor, T1 is the upper power transistor, T2 is the lower power transistor, D1 is the upper freewheeling diode, D2 is the lower freewheeling diode, L is the coil inductance, R is the equivalent resistance, C1 is the upper resonant capacitor, and C2 is the lower resonant capacitor. Detailed Implementation

[0029] This invention discloses a current zero-crossing detection method for a half-bridge series resonant topology, including detection principle, hardware circuit, and judgment logic.

[0030] like Figure 1The diagram shows a half-bridge series resonant topology, where C0 is the bus capacitor, T1 and T2 are the upper and lower power transistors, D1 and D2 are the upper and lower freewheeling diodes, L is the coil inductance, R is the equivalent resistance, and C1 and C2 are the resonant capacitors. The conventional method involves using a current sensor on the cd circuit to detect the coil current, and then using a signal filtering circuit to detect the zero-crossing point of the current signal. The upper and lower power transistors are typically IGBTs, but power MOSFETs or high-power transistors can also be used.

[0031] In a half-bridge series resonant topology, the coil inductance L, equivalent resistance R, and resonant capacitance C1 / C2 are connected in series. The applied excitation is the DC bus voltage. During the conduction period of a power transistor, the inductor current will experience a process of decreasing → crossing zero → increasing in the reverse direction → reaching its peak value → decreasing again. Before the switching transistor is turned off, the inductor current does not cross zero, and the system is in an inductive state, with the current lagging behind the voltage. See Figure 2 The voltage and current state diagram of a half-bridge series resonant topology load operating in inductive state. UL is the inductor voltage, IL is the inductor current, and UC is the capacitor voltage. At time T1, the upper transistor is turned on; at time T2, the inductor current crosses zero; at time T3, the upper transistor is turned off and the lower transistor is turned on; at time T4, the inductor current crosses zero.

[0032] As shown in the figure above, the inductor and capacitor generate an oscillating circuit. When the inductor current crosses zero, the voltage of the resonant capacitor reaches its peak value. Detecting the peak voltage of the resonant capacitor is equivalent to detecting the zero-crossing point of the inductor current.

[0033] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] The first aspect of the present invention provides a current zero-crossing detection device for a half-bridge series resonant topology. The device includes: a voltage sampling circuit connected across a resonant capacitor in a half-bridge converter circuit; the sampling output of the voltage sampling circuit is divided into two sampling output signals with the same phase and amplitude; one sampling output signal is connected to the input of a phase-shifting circuit, and the other sampling output is connected to one input of a comparator circuit; the output of the phase-shifting circuit is connected to the other input of the comparator circuit; the comparator circuit generates a pulse output based on the signals from the two inputs to control the switching elements of the half-bridge converter circuit to turn on or off.

[0035] As described in the first aspect of the invention, the voltage sampling circuit is used to acquire a sinusoidal voltage signal across the resonant capacitor, and the phase shifting circuit shifts the sinusoidal voltage signal ahead of its phase by a predetermined angle.

[0036] As described in the first aspect of the invention, the phase-shifting circuit is an RC sine wave phase-shifting circuit, and the comparison circuit is a two-input comparator.

[0037] As described in the first aspect of the invention, the voltage sampling circuit uses an analog-to-digital converter to sample and convert the voltage across the resonant capacitor; the digital sampling signal output by the voltage sampling circuit is input to a microcontroller, and the microcontroller has built-in circuit modules that form a phase-shifting circuit module and a comparison circuit module to perform phase shifting and comparison on the digital sampling signal to generate the pulse output.

[0038] In the apparatus described in the first aspect of the invention, the voltage sampling circuit is integrated within the microcontroller.

[0039] As described in the first aspect of the present invention, the voltage sampling circuit, phase shifting circuit, and comparison circuit are all built into the microprocessor. The voltage sampling and analog-to-digital conversion module, the phase shifting circuit module, and the comparison circuit module are constructed by the software built into the microprocessor. Under the software control inside the microprocessor, the voltage across the resonant capacitor is sampled, the sampled output signal is phase shifted, and the sampled output signal and the phase-shifted sampled output signal are compared to generate a pulse output.

[0040] A second aspect of the present invention provides a current zero-crossing detection method for a half-bridge series resonant topology, for operating the aforementioned current zero-crossing detection circuit, the method comprising the following steps:

[0041] Step 1: The voltage sampling circuit connected to the two ends of a resonant capacitor in the half-bridge converter circuit detects the sinusoidal voltage across the resonant capacitor and generates two sampling output signals with the same phase and amplitude based on the sinusoidal voltage.

[0042] Step 2: One of the two sampled output signals generated in Step 1 is phase-shifted by a predetermined phase using a phase-shifting circuit to generate a phase-shifted sampled output signal; and the phase-shifted sampled output signal is input to one input of the comparator circuit.

[0043] The other sampling output of the two sampling output signals generated in step 1 is directly connected to the other input of the comparator circuit.

[0044] Step 3: The comparison circuit compares the two input signals and generates a pulse output to control the switching elements of the half-bridge converter circuit to turn on or off.

[0045] As described in the second aspect of the present invention, the phase shifting predetermined phase in step 2 includes obtaining the peak point of the voltage across the resonant capacitor, and using the peak point as a reference, shifting the sinusoidal voltage ahead of the peak point of the voltage across the resonant capacitor by an angle ψ through a phase shifting circuit.

[0046] As described in the second aspect of the present invention, step 3 further includes: generating the rising edge and falling edge of the pulse output at the starting point of the leading ψ angle described in step 2.

[0047] As described in the second aspect of the present invention, when the amplitude of the phase-shifted sampled output signal increases, a rising edge of the pulse output is generated, and when the amplitude of the phase-shifted sampled output signal decreases, a falling edge of the pulse output is generated.

[0048] Example

[0049] Hardware circuit:

[0050] The capacitor voltage is sampled using a resistor to obtain an analog signal. An RC sine wave phase-shifting circuit is built to shift the capacitor voltage sine wave ahead of the sampled signal by a certain angle and compare it with the sampled signal. The output pulse square wave is used for control. See the block diagram of the capacitor voltage phase-shifting circuit. Figure 3 .

[0051] The voltage sampling circuit is used to acquire the sinusoidal voltage signal on capacitor C2. The phase-shifting circuit shifts the capacitor voltage signal ahead by an angle ψ. The signal is then compared with the original waveform by a comparator circuit. When the forward-shifted voltage is greater than the sampled capacitor voltage, the comparator outputs a high level. A schematic diagram of the logic relationship between the forward-shifted voltage and the sampled capacitor voltage is shown below. Figure 4 .

[0052] Judgment logic:

[0053] When the system is working, if the coil inductance parameter is too small, the resonant frequency will shift forward. If the system is controlled at the normal frequency, it is easy to enter the capacitive operating region, which will cause the power transistor to be subjected to inrush current and reduce reliability.

[0054] Therefore, it is necessary to constantly monitor the zero-crossing point of the inductor current during operation. After the hardware detects the zero-crossing point, it participates in the power transistor's turn-off logic. The conventional approach is for the hardware to detect the zero-crossing signal through a current sensor, which is then processed by a signal filtering circuit before reaching the chip. There is a delay in the intermediate process, causing the system to enter the capacitive operating region. Therefore, the hardware detection point needs to be moved forward. Since the zero-crossing point of the inductor current coincides with the peak value of the capacitor voltage, a pulse signal is generated by a phase-shifting circuit to achieve early detection of the current zero-crossing point by an angle ψ (the electrical angle adjustment corresponding to 10% of the switching cycle).

[0055] A phase-shifting circuit is built using resistor R and capacitor C. The basic principle is as follows: Figure 5 A resistor and capacitor are connected in series. When an AC signal Ui is input, this impedance network generates a response current i, producing a voltage drop Uc across the capacitor and a voltage drop Ur across the resistor. The phasor Uc lags the phasor Ur by 90°. The phasors Uc and Ur combine to form the phasor Ui. Therefore, Uo is equal to Ur, and the phasor Ui always lags behind Ur. In other words, the output phasor Uo leads the input phasor Ui, and the phase angle is determined by the RC parameters. This principle can be used to compare the leading signal with the actual signal to obtain the angle ψ.

[0056] RC Lead-Shifting Basic Network

[0057] Depend on Figure 6 As shown, assuming the upper transistor is turned on before the current crosses zero, the current path is as shown by the arrow from left to right. After the current crosses zero, the capacitor goes from charging to discharging, and the inductor current reverses, as shown by the arrow from right to left. If the lower transistor is turned on at this time, the inrush current will be very large and it will be easily damaged. Figure 7 Simplify its current direction diagram.

[0058] According to KVL, u R +u L +u C =u S

[0059] Series current:

[0060]

[0061]

[0062]

[0063] Substituting into the KVL equation and rearranging, we get:

[0064]

[0065] According to formula (1), the capacitor voltage reaches its peak value when the inductor current crosses zero. Depending on the requirements, the ψ angle needs to be controlled in advance before the inductor current crosses zero, because hardware sampling and software processing take 1 to 2 μs. Depending on the different parameters of each resonant network, the current drop range is different. The ψ angle can be adjusted within the electrical angle corresponding to 10% of the switching cycle to be optimal.

[0066] During a switching cycle, when the constant power algorithm is running, if no zero-crossing pulse is detected in the upper switching transistor during the working cycle, the upper transistor will be turned off normally according to the logic. If a zero-crossing pulse is detected during the working cycle, the upper switching transistor will be turned off immediately to prevent it from being turned off after the inductor current crosses zero during the working cycle. Similarly, the lower transistor will be operated on in the same way.

[0067] The function of the lead phase shift circuit is to output a hardware signal before the capacitor voltage reaches its peak point (which is also the zero-crossing point of the inductor current). The system can use this signal for effective closed-loop control. This circuit can be implemented by other circuit methods or by software prediction and estimation.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and are not intended to limit them. Although the embodiments of the present invention have been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the embodiments of the present invention should not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A current zero-crossing detection device for a half-bridge series resonant topology, characterized in that, The device includes: a voltage sampling circuit connected across a resonant capacitor in a half-bridge converter circuit; the sampling output of the voltage sampling circuit is divided into two sampling output signals with the same phase and amplitude; one sampling output signal is connected to the input of a phase-shifting circuit, and the other sampling output is connected to one input of a comparator circuit; the output of the phase-shifting circuit is connected to the other input of the comparator circuit; the phase-shifting circuit is an RC sine wave phase-shifting circuit, and the comparator circuit is a two-input comparator; the comparator circuit generates a pulse output based on the signals from the two inputs to control the switching elements of the half-bridge converter circuit to turn on or off. The voltage sampling circuit is used to acquire the sinusoidal voltage signal across the resonant capacitor. The phase shifting circuit shifts the sinusoidal voltage signal ahead by a predetermined angle. The predetermined phase shift angle can be adjusted within the electrical angle corresponding to 10% of the switching cycle. The phase shifting of the sampled output signal is performed under software control within the microprocessor. The voltage sampling circuit uses an analog-to-digital converter to sample and convert the voltage across the resonant capacitor. The digital sampling signal output by the voltage sampling circuit is input to the microcontroller. The microcontroller has built-in circuit modules that form a phase-shifting circuit module and a comparison circuit module to perform phase shifting and comparison on the digital sampling signal to generate the pulse output.

2. The apparatus as claimed in claim 1, characterized in that, The voltage sampling circuit is built into the microcontroller.

3. The apparatus as described in claim 1, characterized in that, The voltage sampling circuit, phase shifting circuit, and comparator circuit are all built into the microprocessor. The voltage sampling and analog-to-digital conversion module, the phase shifting circuit module, and the comparator circuit module are controlled by the software built into the microprocessor. Under the software control inside the microprocessor, the voltage across the resonant capacitor is sampled, and the sampled output signal is compared with the phase-shifted sampled output signal to generate a pulse output.

4. A method for detecting zero-crossing current in a half-bridge series resonant topology, used to operate the zero-crossing current detection circuit according to any one of claims 1-3, characterized in that, The method includes the following steps: Step 1: The voltage sampling circuit connected to the two ends of a resonant capacitor in the half-bridge converter circuit detects the sinusoidal voltage across the resonant capacitor and generates two sampling output signals with the same phase and amplitude based on the sinusoidal voltage. Step 2: One of the two sampling output signals generated in Step 1 is phase-shifted by a predetermined phase using a phase-shifting circuit to generate a phase-shifted sampling output signal; and the phase-shifted sampling output signal is input to one input of the comparator circuit. The peak point of the voltage across the resonant capacitor is obtained. Using the peak point as a reference, the sinusoidal voltage is shifted by an angle ψ ahead of the peak point of the voltage across the resonant capacitor through a phase-shifting circuit. The other sampling output of the two sampling output signals generated in step 1 is directly connected to the other input of the comparator circuit. Step 3: The comparison circuit compares the two input signals and generates a pulse output to control the switching elements of the half-bridge converter circuit to turn on or off.

5. The method as described in claim 4, characterized in that, Step 3 further includes: generating the rising edge and falling edge of the pulse output from the starting point of the leading ψ angle described in step 2.

6. The method as described in claim 5, characterized in that, When the amplitude of the phase-shifted sampled output signal increases, the rising edge of the pulse output is generated; when the amplitude of the phase-shifted sampled output signal decreases, the falling edge of the pulse output is generated.

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