Pulse density modulated full bridge converter with elimination of specific frequency interharmonics

Abstract

This invention discloses a pulse density modulation full-bridge converter capable of eliminating inter-frequency harmonics, belonging to the field of power electronic control technology. The pulse density modulator provided by this invention includes an adder for adding a pulse density command signal and a feedback signal to obtain a signal to be quantized, x. A quantizer quantizes the signal to be quantized, x, to obtain a pulse signal, a. A register delays pulse signal a by half a switching cycle to generate a pulse signal, b. Pulse signals a and b are input into an XOR gate and then subtracted from the signal to be quantized, x, to obtain a quantization error, e. The quantization error, e, is then filtered by a digital filter to obtain a feedback signal. Pulse signals a and b control the switching state of the full-bridge converter. This invention can be applied to various resonant converters, controlling the converter's output voltage or power through pulse density modulation; it can eliminate inter-frequency harmonics based on the resonant network, avoiding oscillation and ensuring stable converter operation.

Description

Technical Field

[0001] This invention belongs to the field of power electronic control technology; specifically, it relates to a pulse density modulation full-bridge converter that can eliminate inter-harmonics at specific frequencies. Background Technology

[0002] In the field of power electronics control technology, high power density, high efficiency, and low cost converters are more competitive. Most high power density and high efficiency power electronic converters use resonant topologies to achieve soft switching. The resonant circuit can achieve zero-voltage turn-on of two or more primary-side switching transistors and zero-current turn-off of secondary-side rectifier diodes, thereby reducing switching losses and improving the efficiency and power density of the power electronic converter.

[0003] Modulation methods for high-power-density, high-efficiency power electronic converters include pulse frequency modulation (PWM), pulse width modulation (PWM), and pulse density modulation (PDM). PWM can lead to detuning and circulating current, increasing the converter's resistive losses. PWM may disrupt soft-switching conditions and increase switching losses. Pulse density modulation may cause interharmonic oscillations in the resonant network. In summary, existing modulation methods have various shortcomings and limitations. Some resonant converters, such as the LLC DCX converter, sacrifice modulation capabilities to maintain high efficiency and stability, operating only in open-loop mode. Summary of the Invention

[0004] To address the modulation requirements of high-power-density, high-efficiency resonant converters, this invention proposes a pulse density modulation full-bridge converter capable of eliminating interharmonics at specific frequencies. This converter operates in a fixed-frequency soft-switching state, exhibiting rapid modulation response and avoiding the excitation of interharmonic oscillations in the resonant network. It is suitable for closed-loop control of resonant topologies such as SRC, LLC, and CLLC over a wide load range.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies, comprising a pulse density modulator and a full-bridge converter;

[0007] The pulse density modulator includes an adder for adding the pulse density command signal d to the feedback signal to generate the signal to be quantized x, which is then input into the quantizer.

[0008] A quantizer is used to quantize the signal x to be quantized into a pulse signal a based on the polarity of the switching frequency synchronization pulse c.

[0009] The quantization noise feedback loop is used to input the pulse signal a into the register, generate the pulse signal b after delay, input the pulse signal a and the pulse signal b into the XOR gate, and then subtract the signal to be quantized x from the subtractor to obtain the quantization error e. The quantization error e is filtered by a digital filter to obtain the feedback signal, and the feedback signal is input into the adder.

[0010] The leading arm of the full-bridge converter is composed of switches S1 and S2 connected in series, and the lagging arm is composed of switches S3 and S4 connected in series. The switching state of switch S1 is determined by pulse signal a, and the switching state of switch S3 is determined by pulse signal b.

[0011] The quantizer includes a comparator, which is used to output a Boolean value s after comparing the signal x to be quantized. The switching frequency synchronization pulse c and the Boolean value s are input into a first AND gate. At the same time, the Boolean value s is fed into a second AND gate after passing through an NOT gate and then into a second AND gate with a pulse signal b. The output signals of the first AND gate and the second AND gate are fed into an OR gate to obtain a pulse signal a.

[0012] Furthermore, the comparator has a built-in comparison condition that the signal to be quantized, x, is greater than 0.

[0013] Furthermore, the transfer function set in the digital filter is NTF(z)⁻¹, and the transfer function satisfies the following condition:

[0014] 1) NTF(∞) = 1; 2) NTF(1) = 0; 3) NTF contains conjugate zeros located at exp(jπf / fs) and exp(-jπf / fs);

[0015] Where fs is the switching frequency and f is the interharmonic frequency to be eliminated.

[0016] Furthermore, both the register and the digital filter are synchronously triggered by the rising and falling edges of the switching frequency synchronization pulse c.

[0017] Furthermore, the leading arm and the lagging arm are connected in parallel between the DC voltage v and the reference ground, and the voltage between the switching node A of the leading arm and the switching node B of the lagging arm is the inverter output voltage u.

[0018] Furthermore, a preset dead time is added between the upper and lower switches of the leading and lagging bridge arms.

[0019] A method for operating a pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies includes the following steps:

[0020] Both the register and the digital filter are synchronously triggered by the rising and falling edges of the switching frequency synchronization pulse c;

[0021] The pulse density command signal d and the feedback signal are added together to generate the signal to be quantized x;

[0022] The signal to be quantized x is compared to generate a Boolean value s. The Boolean value s and the switching frequency synchronization pulse c are ANDed. At the same time, the Boolean value s is NOTed and then ANDed with the pulse signal b. The two output signals after the AND operation are ORed to generate the pulse signal a.

[0023] After a delay, pulse signal a generates pulse signal b. Pulse signal a and pulse signal b are XORed and then subtracted from the signal to be quantized x to generate quantization error e. Quantization error e passes through a digital filter with transfer function NTF(z)-1 to obtain a feedback signal. The feedback signal is then subtracted from the pulse density command signal d.

[0024] Pulse signal a determines the switching state of switch S1, and the switching state of switch S2 is the opposite of that of switch S1. Pulse signal b determines the switching state of switch S3, and the switching state of switch S4 is the opposite of that of switch S3.

[0025] Furthermore, the pulse density command signal d takes the value of any real number between 0 and 1.

[0026] Furthermore, the pulse signal a is delayed by half a switching cycle to obtain the pulse signal b.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The pulse density modulation full-bridge converter provided by this invention can eliminate inter-frequency harmonics based on the resonant network, avoid oscillation, and ensure stable operation of the converter. The converter always operates in a fixed-frequency soft-switching state, without detuning or hard switching, and has high conversion efficiency. It can be applied to various resonant converters, and the output voltage or power of the converter can be controlled by pulse density modulation.

[0029] Furthermore, by simply adjusting the position of the conjugate zero of the transfer function NTF(z)-1 in the digital filter, interharmonics of a specific frequency can be eliminated. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below:

[0031] Figure 1 This is a structural diagram of the pulse density modulation full-bridge converter of the present invention;

[0032] Figure 2 The following are the output voltage and frequency spectrum of a conventional pulse density modulated full-bridge converter at a pulse density d = 0.8: (a) is the output voltage of the full-bridge converter; (b) is the frequency spectrum of the full-bridge converter.

[0033] Figure 3 The pulse density modulation full-bridge converter of the present invention aims to eliminate the inter-harmonics of 0.8 times the switching frequency when the pulse density d = 0.8. (a) is the frequency characteristic of the noise transfer function; (b) is the output voltage of the full-bridge converter; (c) is the spectrum of the full-bridge converter. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0035] like Figure 1 As shown, a pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies includes a pulse density modulator and a full-bridge converter.

[0036] The pulse density modulator includes an adder 1, a quantization noise feedback loop, and a quantizer. The quantizer is composed of combinational logic gates, including a comparator 2, an NOT gate 3, a first AND gate 4, a second AND gate 5, and an OR gate 6. The quantization noise feedback loop includes a register 7, an XOR gate 8, a subtractor 9, and a digital filter 10.

[0037] The pulse density modulator has two input signals, including a switching frequency synchronization pulse c and a pulse density command signal d.

[0038] Adder 1 is used to add the pulse density command signal d and the feedback signal to obtain the signal to be quantized x, which is then sent to the quantizer.

[0039] A quantizer is used to quantize the signal x to be quantized into a pulse signal a with a value of 0 or 1, based on the polarity of the switching frequency synchronization pulse c.

[0040] The quantizer includes comparator 2, which is used to input the signal to be quantized x into comparator 2, compare it with the comparison condition built into comparator 2, and output a Boolean value s. The comparison condition built into comparator 2 is whether the signal to be quantized x is greater than 0. The Boolean value s and the switching frequency synchronization pulse c are input into the first AND gate 4. At the same time, the Boolean value s is input into the NOT gate 3, and then input into the second AND gate 5 with the pulse signal b. The output signals of the first AND gate 4 and the second AND gate 5 are passed through the OR gate 6 to obtain the pulse signal a.

[0041] The quantization noise feedback loop is used to generate pulse signal b by delaying pulse signal a by half a switching cycle, XORing pulse signal a and pulse signal b, subtracting the signal to be quantized x, and then passing it through a digital filter to generate a feedback signal for input to adder 1.

[0042] The quantization noise feedback loop includes register 7, which delays the pulse signal a by half a switching cycle to obtain pulse signal b. Pulse signal a and pulse signal b pass through XOR gate 8 and then through subtractor 9 to subtract the signal to be quantized x to obtain quantization error e. Quantization error e passes through a digital filter 10 with transfer function NTF(z)-1 to obtain feedback signal. The feedback signal is input to adder 1 to form a closed loop.

[0043] The transfer function satisfies the following conditions: 1) NTF(∞) = 1; 2) NTF(1) = 0; 3) NTF contains conjugate zeros located at exp(jπf / fs) and exp(-jπf / fs);

[0044] Where fs is the switching frequency and f is the interharmonic frequency to be eliminated.

[0045] To eliminate interharmonics at a specific frequency, simply adjust the NTF parameters according to the three conditions mentioned above.

[0046] Register 7 and digital filter 10 are both triggered synchronously by the rising and falling edges of the switching frequency synchronization pulse c.

[0047] The input signal to the modulator is a pulse density command signal d, which takes the value of any real number between 0 and 1.

[0048] The leading arm of the full-bridge converter consists of switches S1 and S2 connected in series, and the lagging arm consists of switches S3 and S4 connected in series. The two arms are connected in parallel between the DC voltage v and the reference ground. The voltage between switch node A of the leading arm and switch node B of the lagging arm is the inverter output voltage u. The switching state of S1 is determined by pulse signal a, the switching state of S2 is the opposite of S1, the switching state of S3 is determined by pulse signal b, and the switching state of S4 is the opposite of S3. A preset dead time is added between the upper and lower switches of the same arm to ensure that shoot-through does not occur.

[0049] A method for operating a pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies is as follows:

[0050] Both the register and the digital filter are synchronously triggered by the rising and falling edges of the switching frequency synchronization pulse c;

[0051] The pulse density command signal d and the feedback signal are input into adder 1 and added to obtain the signal to be quantized x.

[0052] The signal to be quantized, x, is input to comparator 2. After comparison with the built-in comparison conditions of comparator 2, a Boolean value s is generated. Boolean value s and the switching frequency synchronization pulse c are input to the first AND gate 4 for AND operation. At the same time, Boolean value s is input to NOT gate 3 for NOT operation, and then input to the second AND gate 5 for AND operation with the pulse signal b. The output signal after the AND operation of the first AND gate 4 and the second AND gate 5 is input to OR gate 6 for OR operation to generate pulse signal a.

[0053] Pulse signal a is input to register 7 and after a delay of half a switching cycle, pulse signal b is generated. Pulse signal a and pulse signal b are input to XOR gate 8 for XOR operation, and then input to subtractor 9 to subtract the signal to be quantized x to obtain quantization error e. Quantization error e passes through a digital filter 10 with transfer function NTF(z)-1 to obtain feedback signal. Feedback signal is input to adder 1 and added to pulse density command signal d.

[0054] Pulse signal a determines the switching state of switch S1, and the switching state of switch S2 is the opposite of that of switch S1. Pulse signal b determines the switching state of switch S3, and the switching state of switch S4 is the opposite of that of switch S3.

[0055] Example

[0056] like Figure 2 As shown, the output waveform and spectrum of a traditional pulse density modulation converter based on first-order ΔΣ modulation are displayed when the pulse density command d = 0.8. The converter outputs four consecutive square waves with a switching cycle interval, and the output pulse density satisfies the modulation target of d = 0.8. The fundamental amplitude of the AC voltage is equal to the pulse density, but its spectrum contains interharmonics at 0.2, 0.4, 0.6, 0.8, 1.2, 1.4, 1.6, and 1.8 times the switching frequency.

[0057] If the goal is to eliminate the interharmonics at 0.8 times the switching frequency, according to the present invention, a noise transfer function can be designed as follows:

[0058]

[0059] Here, the zeros of NTF are located at exp(j0.2π) and exp(-j0.2π). At this time, the output waveform and spectrum of the converter of this invention are as follows: Figure 3 As shown, the period of the AC side voltage waveform is readjusted, and its pulse density still satisfies the modulation target of d = 0.8. From the spectrum, the fundamental amplitude of the AC side voltage is still equal to the pulse density, but its spectrum no longer contains interharmonics of 0.8 times and 1.2 times the switching frequency, thus achieving the design goal of eliminating the interharmonics of 0.8 times the switching frequency.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending approval.

Claims

1. A pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies, characterized in that, Includes pulse density modulators and full-bridge converters; The pulse density modulator includes an adder for adding the pulse density command signal d to the feedback signal to generate the signal to be quantized x, which is then input into the quantizer. A quantizer is used to quantize the signal to be quantized x into a pulse signal a according to the polarity of the switching frequency synchronization pulse c. The quantizer includes a comparator, which outputs a Boolean value s after comparing the signal to be quantized x. The switching frequency synchronization pulse c and the Boolean value s are input into a first AND gate. At the same time, the Boolean value s is fed into a second AND gate after passing through an NOT gate and then fed into a second AND gate with a pulse signal b. The output signals of the first AND gate and the second AND gate are fed into an OR gate to obtain the pulse signal a. The quantization noise feedback loop is used to input the pulse signal a into the register, generate the pulse signal b after delay, input the pulse signal a and the pulse signal b into the XOR gate, and then subtract the signal to be quantized x from the subtractor to obtain the quantization error e. The quantization error e is passed through the digital filter to obtain the feedback signal, and the feedback signal is input into the adder. The transfer function set in the digital filter is NTF(z)-1, and the transfer function satisfies the following conditions: 1) NTF(∞)=1; 2) NTF(1)=0; 3) NTF contains conjugate zeros located at exp(jπf / fs) and exp(-jπf / fs). Where fs is the switching frequency and f is the interharmonic frequency to be eliminated; The leading arm of the full-bridge converter is composed of switches S1 and S2 connected in series, and the lagging arm is composed of switches S3 and S4 connected in series. The switching state of switch S1 is determined by pulse signal a, and the switching state of switch S3 is determined by pulse signal b.

2. A pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies according to claim 1, characterized in that, The comparator has a built-in comparison condition that the signal to be quantized, x, is greater than 0.

3. A pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies according to claim 1, characterized in that, Both the register and the digital filter are synchronously triggered by the rising and falling edges of the switching frequency synchronization pulse c.

4. A pulse density modulation full-bridge converter capable of eliminating inter-harmonic frequencies according to claim 1, characterized in that, The leading arm and the lagging arm are connected in parallel between the DC voltage v and the reference ground. The voltage between the switching node A of the leading arm and the switching node B of the lagging arm is the inverter output voltage u.

5. A pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies according to claim 1, characterized in that, A preset dead time is added between the upper and lower switches of the leading and lagging bridge arms.

6. A method for operating a pulse density modulation full-bridge converter capable of eliminating interharmonics at specific frequencies, characterized in that, Includes the following steps: Both the register and the digital filter are synchronously triggered by the rising and falling edges of the switching frequency synchronization pulse c; The pulse density command signal d and the feedback signal are added together to generate the signal to be quantized x; The signal to be quantized x is compared to generate a Boolean value s. The Boolean value s and the switching frequency synchronization pulse c are ANDed. At the same time, the Boolean value s is NOTed and then ANDed with the pulse signal b. The two output signals after the AND operation are ORed to generate the pulse signal a. After a delay, pulse signal a generates pulse signal b. Pulse signal a and pulse signal b are XORed and then subtracted from the signal to be quantized x to generate quantization error e. Quantization error e passes through a digital filter with transfer function NTF(z)-1 to obtain a feedback signal. The feedback signal is then subtracted from the pulse density command signal d. The transfer function satisfies the following conditions: 1) NTF(∞) = 1; 2) NTF(1) = 0; 3) NTF contains conjugate zeros located at exp(jπf / fs) and exp(-jπf / fs); Where fs is the switching frequency and f is the interharmonic frequency to be eliminated; Pulse signal a determines the switching state of switch S1, and the switching state of switch S2 is the opposite of that of switch S1. Pulse signal b determines the switching state of switch S3, and the switching state of switch S4 is the opposite of that of switch S3.

7. The operating method of a pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies according to claim 6, characterized in that, The pulse density command signal d takes the value of any real number between 0 and 1.

8. The operating method of a pulse density modulation full-bridge converter capable of eliminating inter-harmonics at specific frequencies according to claim 6, characterized in that, The pulse signal a is delayed by half a switching cycle to obtain the pulse signal b.

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