Digital frequency modulation type excitation alternating current source and working method thereof

Abstract

The invention relates to a digital frequency modulation type excitation alternating current source and a working method thereof. The digital frequency modulation type excitation alternating current source comprises a voltage regulation circuit, a digital signal processing circuit, a D / A conversion circuit, a proportional amplification circuit, a push-pull amplification circuit, a voltage negative feedback circuit, an overcurrent protection circuit and an anti-self-excitation circuit. The input voltage is converted into the power supply voltage of the digital signal processing circuit through the voltage adjusting circuit; the digital signal processing circuit outputs a sine wave digital signal after receiving the square wave signal, and the sine wave digital signal is converted into an analog signal through the D / A conversion circuit to form a sine fundamental wave signal. The sine fundamental wave signal is subjected to output amplitude and output power amplification through the proportional amplification circuit and the push-pull amplification circuit, and a stable and reliable excitation alternating current signal is output. The frequency C2 of the original sinusoidal signal is changed by changing the frequency C1 of the input square wave or pulse signal, and the frequency C2 at the moment is not influenced by the parameter precision of a peripheral circuit, so that the stability of the frequency of the output excitation signal is improved.

Description

Technical Field

[0001] The invention relates to the technical field of excitation AC sources, and in particular to a digital frequency modulation type excitation AC source and a working method thereof. Background Art

[0002] Excitation AC sources are widely used in servo systems, radar systems, navigation control systems and other scenarios. The operating mechanisms of these systems mostly use resolvers to output sine and cosine signals of the rotation angle, and then the accurate rotation angle of the operating mechanism is obtained by resolving the sine and cosine signals to achieve precise control of the operating mechanism. The excitation AC source provides a stable excitation reference signal for the resolver. The stability of the excitation reference signal is related to the quality of the sine and cosine signals output by the resolver, which in turn affects the precise control of the operating mechanism.

[0003] Currently, most excitation AC sources are implemented in two ways: one is to use an oscillation circuit (such as an RC oscillation circuit) to generate a fundamental signal, and then output an excitation AC signal with a certain load capacity through a power amplifier circuit; the other is to use a digital circuit to generate an original sinusoidal signal, and then output the excitation AC signal through a power amplifier circuit. The former is a traditional excitation AC source implementation method, and its change of fundamental signal frequency must be achieved by adjusting hardware parameters, which is more troublesome for excitation AC sources with fixed hardware, and the fundamental signal generated by the oscillation circuit has poor frequency consistency, and has high requirements for the accuracy and stability of resistance and capacitance parameters; the latter is a new excitation source implementation method in recent years, and the frequency change of the original sinusoidal signal can be achieved through software without changing hardware parameters. For example, Chinese patent document CN117277970A uses this method to modify the excitation signal frequency, but this method requires re-modifying the program and burning it into the digital chip to achieve the change of the excitation frequency. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the object of the present invention is to provide a digital frequency modulation excitation AC source and a working method thereof.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A digital frequency modulation excitation AC source comprises a voltage adjustment circuit, a digital signal processing circuit, a D / A conversion circuit, a proportional amplifier circuit, a push-pull amplifier circuit, a voltage negative feedback circuit, an overcurrent protection circuit and an anti-self-excitation circuit.

[0007] The input end of the voltage adjustment circuit is connected to the input voltage, and the output end is connected to the input end of the digital signal processing circuit; the output end of the digital signal processing circuit is connected to the input end of the D / A conversion circuit; the output end of the D / A conversion circuit is connected to the input end of the proportional amplifier circuit; the output end of the proportional amplifier circuit is connected to the input end of the push-pull amplifier circuit; the output end of the push-pull amplifier circuit outputs an excitation AC signal; the input voltage is also input into the push-pull amplifier circuit.

[0008] The voltage negative feedback circuit is used to form voltage negative feedback with the excitation AC signal and the proportional amplifier circuit; the input end of the overcurrent protection circuit is connected to the output end of the push-pull amplifier circuit; the output end of the anti-self-excitation circuit is connected to the input end of the proportional amplifier circuit; the anti-self-excitation circuit is used to prevent the circuit from generating self-oscillation, so that the output excitation signal is more stable.

[0009] Furthermore, the voltage adjustment circuit includes a voltage regulator U1, a capacitor C1, a capacitor C2, a resistor R1, a resistor R2, a capacitor C3 and a capacitor C4. The voltage regulator U1 adopts an LDO chip, and the LDO chip includes an enable terminal EN, two input terminals IN, a ground terminal GND, a feedback terminal FB, two output terminals OUT and a noise reduction port NR. The enable terminal EN of the LDO chip is grounded via capacitor C2; the first terminal of the capacitor C2 is connected to the input voltage Vin1, and the second terminal is grounded; the noise reduction port NR of the LDO chip is grounded via capacitor C1; the two input terminals IN of the LDO chip are both connected to the input voltage Vin1; the ground terminal GND of the LDO chip is grounded; the feedback terminal FB of the LDO chip is grounded via resistor R1; the two output terminals of the LDO chip are both connected to the output voltage Vout1; the first terminal of the resistor R1 is grounded, and the second terminal is respectively connected to the feedback terminal FB of the LDO chip and the first terminal of the resistor R2 and the first terminal of the capacitor C3; the second terminal of the resistor R2, the second terminal of the capacitor C3, and the second terminal of the capacitor C4 are all connected to the output voltage Vout1; the first terminal of the capacitor C4 is grounded.

[0010] Furthermore, the capacitor C2 and the capacitor C4 are decoupling capacitors.

[0011] Furthermore, the digital signal processing circuit includes a digital processor; the D / A conversion circuit includes a D / A conversion chip; the input end of the digital processor is connected to the output voltage Vout1 of the voltage adjustment circuit, and the output end is connected to the digital input port of the D / A conversion chip; the input of the digital processor is a square wave or pulse signal s1 with a frequency of C1, and the output is a sinusoidal digital value output; the input of the D / A conversion chip is a sinusoidal digital value, and the output is an original sinusoidal signal s2 with a frequency of C2.

[0012] Furthermore, the proportional amplifier circuit includes two stages, namely, a primary amplifier circuit and a secondary amplifier circuit. The primary amplifier circuit includes an amplifier U1, a resistor R3, a resistor R4 and a resistor R5; the secondary amplifier circuit includes an amplifier U2, a resistor R6, a current limiting resistor R7, a resistor R8, a resistor R9 and a DC blocking capacitor C6; and the excitation signal output by the push-pull amplifier and the resistor R9 and the amplifier U2 form the voltage negative feedback circuit.

[0013] The anti-self-excitation circuit is implemented by capacitor compensation in the Miller effect compensation method, and the anti-self-excitation circuit includes capacitor C5 and capacitor C7; the output end and input end of the primary amplifier circuit and the secondary amplifier circuit are connected through capacitor C5 and capacitor C7 respectively; the voltage negative feedback circuit connects the output end of the push-pull amplifier circuit with the reverse input end of the secondary amplifier circuit through the resistor R9; the input voltage is also input into the push-pull amplifier circuit.

[0014] The positive input terminal of the first amplifier U1 is grounded via resistor R5, the negative input terminal of the first amplifier U1 is connected to the output signal of the D / A conversion circuit via resistor R3, the output terminal of the first amplifier U1 is respectively connected to the first end of the current limiting resistor R7 and the second end of the resistor R4; the first end of the resistor R4 is connected to the negative input terminal of the first amplifier U1; the second end of the current limiting resistor R7 is connected to the negative input terminal of the second amplifier U2 via the DC blocking capacitor C6; the negative input terminal of the second amplifier U2 is respectively connected to the first end of the resistor R8, the first end of the resistor R9, and the first end of the capacitor C7; the positive input terminal of the second amplifier U2 is grounded via resistor R6; the output terminal of the second amplifier U2 is connected to the second end of the capacitor C7; the second end of the resistor R8 is grounded; the second end of the resistor R9 is connected to the output terminal of the entire excitation AC source.

[0015] Furthermore, the push-pull amplifier circuit includes a resistor R11, a resistor R12, a resistor R13, a resistor R14, a capacitor C8, a capacitor C9, a diode D1, a diode D2, a transistor Q1 and a transistor Q2; the resistor R13 and the resistor R14 are power resistors.

[0016] The overcurrent protection circuit includes a resistor R13, a resistor R14, a diode D3, a diode D4, a transistor Q3 and a transistor Q4; the bases of the control-end transistors Q3 and Q4 of the overcurrent protection circuit are connected to the output end of the push-pull amplifier circuit through the resistor R13 and the resistor R14 respectively.

[0017] The first end of the resistor R11, the first end of the capacitor C9 and the collector of the transistor C1 are all connected to the positive end of the power supply; the second end of the resistor R11 is connected to the anode of the diode D1; the cathode of the diode D1 is connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the first end of the resistor R12; the second end of the resistor R12, the second end of the capacitor C8 and the collector of the transistor Q3 are all connected to the negative end of the power supply; the second end of the capacitor C9 is respectively connected to the second end of the resistor R11, the anode of the diode D3, and the base of the transistor Q1; the cathode of the diode D3 is connected to the collector of the transistor Q3; the base of the transistor Q3 is respectively connected to the emitter of the transistor Q1, the cathode of the resistor R11 and the collector of the transistor Q3; the cathode of the diode D3 is connected to the collector of the transistor Q3; the cathode of the transistor Q3 is respectively connected to the emitter of the transistor Q1, the cathode of the resistor R12 and the collector of the transistor Q3; the cathode of the diode D3 is connected to the collector of the transistor Q3; the cathode ... diode D2 and the collector of the transistor Q3; the cathode of the transistor 13 is connected to the first end of the resistor R13; the emitter of the transistor Q3 is connected to the second end of the resistor R13 and the emitter of the transistor Q4 respectively; the collector of the transistor Q4 is connected to the anode of the diode D4, and the base of the transistor Q4 is connected to the second end of the resistor R14 and the emitter of the transistor Q2 respectively; the cathode of the diode D4 is connected to the first end of the capacitor C8, the first end of the resistor R12, the cathode of the diode D2, and the base of the transistor Q2 respectively; the emitter of the transistor Q1 is connected to the first end of the resistor R13, the second end of the resistor R13 is connected to the first end of the resistor R14, and the second end of the resistor R14 is connected to the emitter of the transistor Q2.

[0018] Furthermore, the digital processor adopts FPGA.

[0019] Furthermore, the resistor R11 and the resistor R12 are current limiting resistors; the resistor R13 and the resistor R14 are power resistors; the diode D1 and the diode D2 are high-speed switching diodes; the transistor Q1 and the transistor Q2 are Darlington transistors; and the transistor Q3 and the transistor Q4 are thyristors.

[0020] The present invention also includes a working method of the above-mentioned digital frequency modulation excitation AC source, the method comprising the following steps:

[0021] S1. The input voltage is converted into the power supply voltage of the digital signal processing circuit through the voltage adjustment circuit.

[0022] S2. After receiving the square wave signal, the digital signal processing circuit outputs a sinusoidal digital signal. The sinusoidal digital signal is converted into an analog signal through a D / A conversion circuit to form a sinusoidal fundamental wave signal.

[0023] S3. The fundamental sinusoidal wave signal is amplified by the first-stage amplifier circuit for output amplitude amplification, and is processed by the second-stage amplifier circuit for voltage negative feedback and stable amplification factor to output a sinusoidal signal; the second-stage amplifier circuit is used for voltage negative feedback and stable amplification factor to improve the dynamic performance of the circuit (the amplification factor of the second-stage amplifier circuit is generally set to 1).

[0024] S4. The sinusoidal signal output by the secondary amplifier circuit is amplified by the push-pull amplifier circuit to amplify the output power and output the required excitation AC signal.

[0025] S5. When the circuit is overloaded, a large current is generated, and the voltage across the resistors R13 and R14 increases, reaching the turn-on voltage of the transistors Q3 and Q4; the overcurrent protection circuit starts to work, and the output of the amplifier circuit is cut off to protect the subsequent circuit; the anti-self-excitation circuit prevents the circuit from generating self-excitation oscillation, and is used to make the output excitation signal more stable.

[0026] Furthermore, in step S2, the digital signal processing circuit outputs a sinusoidal digital signal after receiving the square wave signal, and the sinusoidal digital signal is converted into an analog signal by a D / A conversion circuit to form a sinusoidal fundamental signal, including:

[0027] S21. Use a digital processor to divide and count the input square wave signal, determine the frequency of the sine wave, and output a sine signal.

[0028] S22. Use the IP core of the digital processor to establish a memory, digitally encode the standard sinusoidal signal; sample a period of the sinusoidal signal, and represent the corresponding sinusoidal output with a decimal value; at the same time, encode the address and use hexadecimal numbers to represent it, so that the address and the output sinusoidal value form a mapping relationship, build a sine table, and store the sine table in the memory.

[0029] S23, using the pulse signal generated by the active crystal oscillator of the digital processor as the clock base frequency, performing serial data shift and storage on the sinusoidal signal, and outputting the sinusoidal digital value.

[0030] S24. The sine table in the memory is converted into an analog sine waveform through a D / A conversion circuit to generate an excitation signal of a corresponding frequency, thereby forming a sine fundamental wave signal.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) The digital frequency modulation excitation AC source described in the present invention has an input voltage that is converted into a power supply voltage for a digital signal processing circuit through a voltage adjustment circuit; the digital signal processing circuit outputs a sinusoidal digital signal after receiving a square wave signal, and the sinusoidal digital signal is converted into an analog signal through a D / A conversion circuit to form a sinusoidal fundamental signal. The sinusoidal fundamental signal is amplified in output amplitude and output power through a proportional amplifier circuit and a push-pull amplifier circuit, and finally a stable and reliable excitation AC signal is output. In the digital frequency modulation excitation AC source described in the present invention, protection measures such as voltage negative feedback, overcurrent protection circuit, and anti-self-excitation circuit are added; voltage negative feedback can stabilize the amplification factor and improve the dynamic performance of the circuit; when the circuit is overloaded, a large current will be generated, at which time the overcurrent protection circuit starts to work, and the push-pull amplifier circuit cuts off the output, effectively protecting the subsequent circuit; the anti-self-excitation circuit can effectively prevent the circuit from generating self-excitation oscillation, making the output excitation signal more stable.

[0033] (2) The present invention uses an FPGA digital processor (other digital signal processors such as MCU, DSP, CPLD, etc. may also be used). A sine table is first written into the memory. Each sine value in the sine table has a corresponding address code. A square wave or pulse signal with a frequency of C1 is input from the periphery. The pulse signal generated by the active crystal oscillator is used as the clock base frequency to perform serial data shifting and storage, and output the sine digital value. Through the D / A conversion circuit, the sine table in the memory is converted into an analog sine waveform to generate an original sine signal with a frequency of C2. The original sine signal then passes through the power amplifier circuit to output an excitation AC signal. The frequency of the excitation AC signal at this time is C2. In the present invention, the frequency C2 of the original sine signal can be changed by changing the frequency C1 of the input square wave or pulse signal, and the frequency C2 at this time is not affected by the accuracy of the peripheral circuit parameters, thereby improving the stability of the output excitation signal frequency.

[0034] (3) It is relatively troublesome to change the frequency of the existing excitation source circuit. The RC oscillation method requires adjusting the parameters of the hardware circuit, and the traditional digital method requires re-burning the program. The present invention is based on the traditional digital excitation source. It does not need to change the program. It only needs to change the frequency C1 of the external input square wave or pulse signal. The output excitation signal is not affected by the accuracy of the peripheral circuit parameters. The consistency and stability of the product are guaranteed from the hardware and software. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a principle block diagram of the digital frequency modulation excitation AC source in the present invention;

[0036] Figure 2 It is a circuit principle diagram of the voltage regulating circuit in the present invention;

[0037] Figure 3It is a circuit principle diagram of a digital signal processing circuit and a D / A conversion circuit in the present invention;

[0038] Figure 4 It is a circuit principle diagram of the proportional amplification circuit, voltage negative feedback and anti-self-excitation circuit in the present invention;

[0039] Figure 5 It is a circuit principle diagram of the push-pull amplifier circuit and the overcurrent protection circuit in the present invention;

[0040] Figure 6 It is a flow chart of the implementation method of the original sinusoidal signal s2 in the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings:

[0042] Excitation AC sources are widely used in servo systems, radar systems, navigation control systems and other scenarios to provide a reliable and stable excitation signal for the system. In different scenarios, the frequencies of the excitation signals used in different systems may be different. The present invention proposes a digital frequency modulation excitation AC source and a working method thereof.

[0043] like Figure 1 A digital frequency modulation excitation AC source is shown, which includes a voltage adjustment circuit, a digital signal processing circuit, a D / A conversion circuit, a proportional amplifier circuit, and a push-pull amplifier circuit. In addition, the digital frequency modulation excitation AC source circuit adds voltage negative feedback, overcurrent protection, and anti-self-excitation protection measures, which are achieved through voltage negative feedback circuits, overcurrent protection circuits, and anti-self-excitation circuits. The input end of the voltage regulating circuit is connected to the input voltage, and the output end is connected to the input end of the digital signal processing circuit; the output end of the digital signal processing circuit is connected to the input end of the D / A conversion circuit; the output end of the D / A conversion circuit is connected to the input end of the proportional amplifier circuit; the output end of the proportional amplifier circuit is connected to the input end of the push-pull amplifier circuit; the output end of the push-pull amplifier circuit outputs an excitation AC signal; the proportional amplifier circuit includes a primary amplifier circuit and a secondary amplifier circuit; the anti-self-excitation circuit adopts the capacitor compensation in the Miller effect compensation method, and the output end and input end of the primary amplifier circuit and the secondary amplifier circuit are connected through capacitor C5 and capacitor C7 respectively; the voltage negative feedback is to connect the output end of the push-pull amplifier circuit with the reverse input end of the secondary amplifier circuit through resistor R9; the bases of the control end transistors Q3 and Q4 of the overcurrent protection circuit are connected to the output end of the push-pull amplifier circuit through power resistors R13 and power resistors R14 respectively; the input voltage is also input into the push-pull amplifier circuit.

[0044] The input voltage is converted into the power supply voltage of the digital signal processing circuit through the voltage adjustment circuit; after receiving the square wave signal, the digital signal processing circuit outputs a sinusoidal digital signal, and the sinusoidal digital signal is converted into an analog signal through the D / A conversion circuit to form a sinusoidal fundamental signal. The sinusoidal fundamental signal is amplified in output amplitude and output power through the proportional amplifier circuit and the push-pull amplifier circuit, and finally a stable and reliable excitation AC signal is output. In the digital frequency modulation excitation AC source described in the present invention, protection measures such as voltage negative feedback, overcurrent protection circuit, and anti-self-excitation circuit are added; voltage negative feedback can stabilize the amplification factor and improve the dynamic performance of the circuit; when the circuit is overloaded, a large current will be generated, and the overcurrent protection circuit will start to work at this time, and the push-pull amplifier circuit will cut off the output to effectively protect the subsequent circuit; the anti-self-excitation circuit can effectively prevent the circuit from generating self-excitation oscillation, making the output excitation signal more stable.

[0045] Figure 2 Figure 1 is the circuit schematic diagram of the voltage regulation circuit. Figure 2 As shown, the voltage adjustment circuit includes a voltage regulator U1, a capacitor C1, a capacitor C2, a resistor R1, a resistor R2, a capacitor C3 and a capacitor C4. The voltage regulator U1 adopts an LDO chip, and the LDO chip includes an enable terminal EN, two input terminals IN, a ground terminal GND, a feedback terminal FB, two output terminals OUT and a noise reduction port NR. Capacitors C2 and C4 are decoupling capacitors.

[0046] The enable terminal EN of the LDO chip is grounded via capacitor C2. The first terminal of capacitor C2 is connected to the input voltage Vin1, and the second terminal is grounded. The noise reduction port NR of the LDO chip is grounded via capacitor C1. Both input terminals IN of the LDO chip are connected to the input voltage Vin1. The ground terminal GND of the LDO chip is grounded. The feedback terminal FB of the LDO chip is grounded via resistor R1. Both output terminals of the LDO chip are connected to the output voltage Vout1. The first end of resistor R1 is grounded, and the second end is respectively connected to the feedback terminal FB of the LDO chip and the first end of resistor R2 and the first end of capacitor C3. The second end of resistor R2, the second end of capacitor C3, and the second end of capacitor C4 are all connected to the output voltage Vout1. The first end of capacitor C4 is grounded.

[0047] The voltage adjustment circuit of the present invention uses an LDO chip to convert the input voltage Vin1 into an output voltage Vout1. Vout1 is used to power a digital processor. Since the digital processor has high requirements for power supply quality, decoupling capacitors C2 and C4 need to be added at the input and output ends. Resistors R1 and R2 are proportional resistors for adjusting the output size of Vout1. Digital processors with different input voltage requirements can adjust the output size of the output voltage Vout1 by adjusting the ratio of resistors R1 and R2.

[0048] Figure 3The circuit diagram of the digital signal processing circuit and the D / A conversion circuit is shown in Figure 1. This part of the circuit outputs an original sinusoidal signal s2 with a frequency of C2. Figure 3 As shown, the digital signal processing circuit includes a digital processor; preferably, the digital processor adopts FPGA. The D / A conversion circuit includes a D / A conversion chip. The input terminal of the digital processor is connected to the output voltage Vout1 of the voltage adjustment circuit, and the output terminal is connected to the digital input port of the D / A conversion chip. The input of the digital processor is a square wave or pulse signal s1 with a frequency of C1, and the output is a sinusoidal digital value output. The input of the D / A conversion chip is a sinusoidal digital value, and the output is an original sinusoidal signal s2 with a frequency of C2.

[0049] like Figure 6 As shown, the implementation steps of the above original sinusoidal signal s2 are as follows:

[0050] (1) FPGA frequency division counting: Count the input square wave or pulse. Use a pin of FPGA to read the pulse and trigger it on the rising edge. Set the counter to increase the count value by 1 every time a rising edge is encountered, and the count cycle is used as a cycle (the count value is adjustable) to output the relevant signal frequency.

[0051] (2) Address encoding: Use the FPGA IP core to build a memory and digitally encode the standard sinusoidal signal. Sample a period of the sinusoidal signal, and the corresponding sinusoidal output is represented by a decimal value. At the same time, encode the address and use hexadecimal numbers to form a mapping relationship between the address and the sinusoidal value. The constructed sine table is stored in the memory.

[0052] (3) D / A conversion circuit: The conversion circuit is composed of a D / A conversion chip and peripheral resistors and capacitors. The pulse signal generated by the active crystal oscillator is used as the clock base frequency to shift and store serial data and output the sinusoidal digital value. The D / A conversion circuit converts the sine table in the memory into an analog sine waveform to generate an excitation signal of the corresponding frequency.

[0053] The input square wave signal frequency or pulse frequency of the digital processor is C1, and the relationship between the counter value n and the output signal frequency C2 is: C2 = C1 / n. The present invention can change the frequency C2 of the original sinusoidal signal by changing the frequency C1 of the input square wave or pulse signal without changing the hardware parameters, and the frequency C2 at this time is not affected by the accuracy of the peripheral circuit parameters, thereby improving the stability of the output excitation signal frequency.

[0054] Figure 4 The schematic diagram of the proportional amplifier circuit, voltage negative feedback and anti-self-excitation circuit is shown in Figure 2. Figure 4As shown, the proportional amplifier circuit includes two stages: a primary amplifier circuit and a secondary amplifier circuit. The primary amplifier circuit includes an amplifier U1, a resistor R3, a resistor R4 and a resistor R5; the secondary amplifier circuit includes an amplifier U2, a resistor R6, a current limiting resistor R7, a resistor R8, a resistor R9 and a DC blocking capacitor C6; the excitation signal output by the push-pull amplifier, the resistor R9 and the amplifier U2 form the voltage negative feedback circuit;

[0055] The anti-self-excitation circuit adopts the capacitor compensation in the Miller effect compensation method, and the compensation capacitor includes capacitor C5 and capacitor C7.

[0056] The positive input terminal of the first amplifier U1 is grounded via resistor R5, the negative input terminal of the first amplifier U1 is connected to the output signal of the D / A conversion circuit via resistor R3, the output terminal of the first amplifier U1 is respectively connected to the first end of the current limiting resistor R7 and the second end of the resistor R4; the first end of the resistor R4 is connected to the negative input terminal of the first amplifier U1; the second end of the current limiting resistor R7 is connected to the negative input terminal of the second amplifier U2 via the DC blocking capacitor C6; the negative input terminal of the second amplifier U2 is respectively connected to the first end of the resistor R8, the first end of the resistor R9, and the first end of the capacitor C7; the positive input terminal of the second amplifier U2 is grounded via resistor R6; the output terminal of the second amplifier U2 is connected to the second end of the capacitor C7; the second end of the resistor R8 is grounded; the second end of the resistor R9 is connected to the output terminal of the entire excitation AC source.

[0057] The original sinusoidal signal s2 is amplified by the first-stage amplifier circuit formed by the first amplifier U1 to obtain signal s3. The amplitude conversion relationship between signal s2 and signal s3 is: s3 = -s2*R4 / R3. After the signal s3 passes through the current limiting resistor R7 and the DC blocking capacitor C6, it enters the second-stage amplifier circuit formed by the second amplifier U2 for second-stage amplification to obtain signal s4. The amplitude conversion relationship between signal s4 and signal s3 is: s4 = -s3*R9 / R8. The second-stage amplifier circuit is mainly used for voltage negative feedback, which can stabilize the amplification factor and improve the dynamic performance of the circuit. The amplification factor of the second-stage amplifier circuit is generally set to 1, that is, R9 = R8. According to the capacitor compensation method in Miller effect compensation, a capacitor with a smaller capacitance is added to the output end and the reverse input end of the amplifier in the two-stage amplifier circuit, such as Figure 4 Capacitors C5 and C7 in the circuit. Capacitors C5 and C7 between the output and the reverse input of the two amplifiers can effectively prevent the output signal from self-excitation.

[0058] Figure 5The schematic diagram of the push-pull amplifier circuit and the overcurrent protection circuit. The amplitude and frequency of the above-mentioned S4 signal are basically consistent with the excitation source signal that the present invention ultimately wants, but the carrying capacity of the S4 signal is very small, often only a few mA of current capacity, which is difficult to meet the actual engineering application. In order to improve the carrying capacity of the S4 signal, the present invention uses a push-pull amplification method to improve the carrying capacity of the signal, so that it reaches a current capacity of several hundred mA.

[0059] like Figure 5 As shown, the push-pull amplifier circuit includes a resistor R11, a resistor R12, a resistor R13, a resistor R14, a capacitor C8, a capacitor C9, a diode D1, a diode D2, a transistor Q1, and a transistor Q2. The overcurrent protection circuit includes a resistor R13, a resistor R14, a diode D3, a diode D4, a transistor Q3, and a transistor Q4. The first end of the resistor R11, the first end of the capacitor C9, and the collector of the transistor C1 are all connected to the positive end of the power supply. The second end of the resistor R11 is connected to the anode of the diode D1. The cathode of the diode D1 is connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the first end of the resistor R12. The second end of the resistor R12, the second end of the capacitor C8, and the collector of the transistor Q3 are all connected to the negative end of the power supply. The second end of the capacitor C9 is respectively connected to the second end of the resistor R11, the anode of the diode D3, and the base of the transistor Q1. The cathode of the diode D3 is connected to the collector of the transistor Q3. The base of transistor Q3 is connected to the emitter of transistor Q1 and the first end of resistor R13 respectively. The emitter of transistor Q3 is connected to the second end of resistor R13 and the emitter of transistor Q4 respectively. The collector of transistor Q4 is connected to the anode of diode D4, and the base of transistor Q4 is connected to the second end of resistor R14 and the emitter of transistor Q2 respectively. The cathode of diode D4 is connected to the first end of capacitor C8, the first end of resistor R12, the cathode of diode D2 and the base of transistor Q2 respectively. The emitter of transistor Q1 is connected to the first end of resistor R13, the second end of resistor R13 is connected to the first end of resistor R14, and the second end of resistor R14 is connected to the emitter of transistor Q2.

[0060] In the push-pull amplifier circuit, the resistor R11 and the resistor R12 are current limiting resistors, the diode D1 and the diode D2 are high-speed switching diodes, the transistor Q1 and the transistor Q2 are Darlington transistors, the transistor Q3 and the transistor Q4 are thyristors, and the resistor R13 and the resistor R14 are power resistors.

[0061] The working principle of the push-pull amplifier circuit is:

[0062] In a sine cycle, when the first half of the sine signal s4 enters the circuit, the voltage drop of the high-speed switch diode D1 meets the turn-on requirement of Q1, so Q1 is turned on and s5 outputs the first half signal; when the second half of the sine signal s4 enters the circuit, the voltage drop of D2 meets the turn-on requirement of Q2, so Q2 is turned on and s5 outputs the second half signal. Thus, the final excitation source signal s5 is obtained.

[0063] The working principle of the overcurrent protection circuit is:

[0064] When the output current is too large, the voltage across resistor R13 or resistor R14 increases and reaches the turn-on voltage of Q3 or Q4. At this time, transistor Q3 or transistor Q4 is turned on, the overcurrent protection circuit starts to work, and the push-pull amplifier circuit cuts off the output. At this time, s5 has no output, thereby protecting the power devices in the circuit from damage.

[0065] The working principle of the hardware part of the digital frequency modulation excitation AC source described in the present invention is:

[0066] The input voltage is converted into the power supply voltage of the digital signal processing circuit through the voltage adjustment circuit. After receiving the square wave signal, the digital processor outputs a sinusoidal digital signal, which is converted into an analog signal through the DA conversion circuit to form a sinusoidal fundamental signal. The sinusoidal fundamental signal is amplified by the proportional amplifier circuit and the push-pull amplifier circuit to amplify the output amplitude and output power, and finally outputs a stable and reliable excitation AC signal. Overcurrent protection circuit and anti-self-excitation circuit are added to this part of the circuit. When the circuit is overloaded, a large current will be generated. At this time, the overcurrent protection circuit starts to protect the output and effectively protects the subsequent circuit; the anti-self-excitation circuit can effectively prevent the circuit from self-excited oscillation, making the output excitation signal more stable.

[0067] The software part of the digital frequency modulation excitation AC source described in the present invention is implemented by using an FPGA digital processor, and other digital signal processing circuits such as MCU, DSP, CPLD, etc. can also be used.

[0068] S1. The input voltage is converted into the power supply voltage of the digital signal processing circuit through the voltage adjustment circuit.

[0069] S2. After receiving the square wave signal, the digital signal processing circuit outputs a sinusoidal digital signal. The sinusoidal digital signal is converted into an analog signal through a D / A conversion circuit to form a sinusoidal fundamental wave signal.

[0070] S3. The fundamental sinusoidal wave signal is amplified by the first-stage amplifier circuit for output amplitude amplification, and is processed by the second-stage amplifier circuit for voltage negative feedback and stable amplification factor to output a sinusoidal signal; the second-stage amplifier circuit is used for voltage negative feedback and stable amplification factor to improve the dynamic performance of the circuit (the amplification factor of the second-stage amplifier circuit is generally set to 1).

[0071] S4. The sinusoidal signal output by the secondary amplifier circuit is amplified by the push-pull amplifier circuit to amplify the output power and output the required excitation AC signal.

[0072] S5. When the circuit is overloaded, a large current is generated, and the voltage across the resistors R13 and R14 increases, reaching the turn-on voltage of the transistors Q3 and Q4; the overcurrent protection circuit starts to work, and the output of the amplifier circuit is cut off to protect the subsequent circuit; the anti-self-excitation circuit prevents the circuit from generating self-excitation oscillation, and is used to make the output excitation signal more stable.

[0073] Preferably, in step S2, the digital signal processing circuit outputs a sinusoidal digital signal after receiving the square wave signal, and the sinusoidal digital signal is converted into an analog signal by a D / A conversion circuit to form a sinusoidal fundamental signal, including:

[0074] S21, using a digital processor to perform frequency division counting on the input square wave signal, determine the frequency of the sine wave, and output a sine signal;

[0075] S22, using the IP core of the digital processor to establish a memory, digitally encode the standard sinusoidal signal; sampling a period of the sinusoidal signal, and the corresponding sinusoidal output is represented by a decimal value; at the same time, encoding the address, using a hexadecimal number to represent it, so that the address and the output sinusoidal value form a mapping relationship, constructing a sine table, and storing the sine table in the memory;

[0076] S23, using the pulse signal generated by the active crystal oscillator of the digital processor as the clock base frequency, performing serial data shift and storage on the sinusoidal signal, and outputting the sinusoidal digital value;

[0077] S24. The sine table in the memory is converted into an analog sine waveform through a D / A conversion circuit to generate an excitation signal of a corresponding frequency, thereby forming a sine fundamental wave signal.

[0078] Taking the generation of a 400 Hz sine wave as an example, the digital frequency modulation excitation AC source of the present invention is described in detail:

[0079] It is known that the input signal is a 409.6kHz square wave signal, TTL level. In order to achieve a 400Hz sine output, the sampling interval and sampling accuracy must be considered during the design. Since the frequency of the input signal is 1024 times that of the output signal, the period is 1 / 1024 of it. To facilitate analog-to-digital conversion, the sampling length is a power of 2. From the input-output relationship, it can be seen that the optimal number of sampling points is 1024 points. For the sampled sine value, it is represented by an unsigned decimal number, and the corresponding value range is obtained according to the selected D / A bit number.

[0080] In the design process of digital frequency modulation excitation AC source, programmable logic device (FPGA) is selected to realize signal control and transmission. It has rich memory and high IO rate, which is suitable for high-speed memory control, high-speed interface expansion and conversion, and ensures the stability of output frequency. Different pins need to be configured to realize functions.

[0081] First, write a sine waveform table: sample the sine signal at 1024 points, that is, sample once when each input signal pulse comes. At this time, the sampling interval is the smallest, and the obtained sine waveform is more accurate. Use a 14-bit D / A converter, and the sine value of the sampling point is represented by a 14-bit unsigned decimal number, ranging from 0 to 16383. At the same time, assign each point a corresponding address value, represented by a hexadecimal number, starting from 0 and adding 1 in sequence, to establish a mapping relationship between the address value and the sine value. Next, use the FPGA IP core to establish a memory, import the written sine signal table, and call it when the pulse signal arrives. Use software programming to control the input, output and timing of the chip pins. Use a definable GPIO port to introduce input square wave signals and crystal oscillator signals, and lead out 3 control signals (data clock, digital chip select input and digital input) and 1 output signal (serial digital) to the D / A converter.

[0082] By designing the software part of the digital frequency modulation excitation AC source described in the present invention, the input 409.6KHz square wave is counted, and the count value is increased by 1 every time a rising edge is encountered. The frequency of the output signal is stabilized at 400Hz with a cycle of 1024. At the same time, the sine value corresponding to the address value in the memory is found and output to the D / A converter. The crystal oscillator clock provided to the D / A converter is 25MHz. Since a serial method is adopted, a shift register needs to be set up to shift the 14-bit value in sequence and send it to the D / A. When the FPGA outputs a valid control signal, the D / A converter converts the sine table value into an analog sine wave.

[0083] The present invention uses an FPGA digital processor (other digital signal processors such as MCU, DSP, CPLD, etc. may also be used), firstly writes a sine table in a memory, each sine value in the sine table has a corresponding address code, and peripherally inputs a square wave or pulse signal with a frequency of C1, uses the pulse signal generated by an active crystal oscillator as the clock base frequency, performs serial data shifting and storage, and outputs the sine digital value. Through a D / A conversion circuit, the sine table in the memory is converted into an analog sine waveform to generate an original sine signal with a frequency of C2, and the original sine signal is then output through a power amplifier circuit to output an excitation AC signal, and the frequency of the excitation AC signal at this time is C2. In the present invention, the frequency C2 of the original sine signal can be changed by changing the frequency C1 of the input square wave or pulse signal, and the frequency C2 at this time is not affected by the accuracy of the peripheral circuit parameters, thereby improving the stability of the output excitation signal frequency.

[0084] The above-described embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the scope of protection determined by the claims of the present invention.

Claims

1. A digital frequency modulation excitation AC source, characterized in that: The digital frequency modulation excitation AC source includes a voltage adjustment circuit, a digital signal processing circuit, a D / A conversion circuit, a proportional amplifier circuit, a push-pull amplifier circuit, a voltage negative feedback circuit, an overcurrent protection circuit and an anti-self-excitation circuit; The input end of the voltage regulating circuit is connected to the input voltage, and the output end is connected to the input end of the digital signal processing circuit; the output end of the digital signal processing circuit is connected to the input end of the D / A conversion circuit; the output end of the D / A conversion circuit is connected to the input end of the proportional amplifier circuit; the output end of the proportional amplifier circuit is connected to the input end of the push-pull amplifier circuit; the output end of the push-pull amplifier circuit outputs an excitation AC signal; the input voltage is also input into the push-pull amplifier circuit; The voltage negative feedback circuit is used to form voltage negative feedback with the excitation AC signal and the proportional amplifier circuit; The input end of the overcurrent protection circuit is connected to the output end of the push-pull amplifier circuit; The output end of the anti-self-excitation circuit is connected to the input end of the proportional amplifier circuit; the anti-self-excitation circuit is used to prevent the circuit from generating self-excitation oscillation, so that the output excitation signal is more stable.

2. The digital frequency modulation excitation AC source according to claim 1, characterized in that: The voltage adjustment circuit includes a voltage stabilizer U1, a capacitor C1, a capacitor C2, a resistor R1, a resistor R2, a capacitor C3 and a capacitor C4; The voltage regulator U1 adopts an LDO chip, which includes an enable terminal EN, two input terminals IN, a ground terminal GND, a feedback terminal FB, two output terminals OUT and a noise reduction port NR; The enable terminal EN of the LDO chip is grounded via capacitor C2; the first terminal of the capacitor C2 is connected to the input voltage Vin1, and the second terminal is grounded; the noise reduction port NR of the LDO chip is grounded via capacitor C1; the two input terminals IN of the LDO chip are both connected to the input voltage Vin1; the ground terminal GND of the LDO chip is grounded; the feedback terminal FB of the LDO chip is grounded via resistor R1; the two output terminals of the LDO chip are both connected to the output voltage Vout1; the first terminal of the resistor R1 is grounded, and the second terminal is respectively connected to the feedback terminal FB of the LDO chip and the first terminal of the resistor R2 and the first terminal of the capacitor C3; the second terminal of the resistor R2, the second terminal of the capacitor C3, and the second terminal of the capacitor C4 are all connected to the output voltage Vout1; the first terminal of the capacitor C4 is grounded.

3. The digital frequency modulation excitation AC source according to claim 2, characterized in that: The capacitor C2 and the capacitor C4 are decoupling capacitors.

4. The digital frequency modulation excitation AC source according to claim 1, characterized in that: The digital signal processing circuit includes a digital processor; The D / A conversion circuit includes a D / A conversion chip; The input terminal of the digital processor is connected to the output voltage Vout1 of the voltage adjustment circuit, and the output terminal is connected to the digital input port of the D / A conversion chip; the input of the digital processor is a square wave or pulse signal s1 with a frequency of C1, and the output is a sinusoidal digital value output; The input of the D / A conversion chip is a sinusoidal digital value, and the output is an original sinusoidal signal s2 of frequency C2.

5. The digital frequency modulation excitation AC source according to claim 3, characterized in that: The proportional amplifier circuit includes two stages: a primary amplifier circuit and a secondary amplifier circuit. The primary amplifier circuit includes an amplifier U1, a resistor R3, a resistor R4 and a resistor R5; the secondary amplifier circuit includes an amplifier U2, a resistor R6, a current limiting resistor R7, a resistor R8, a resistor R9 and a DC blocking capacitor C6; the excitation signal output by the push-pull amplifier, the resistor R9 and the amplifier U2 form the voltage negative feedback circuit; The anti-self-excitation circuit is implemented by capacitor compensation in the Miller effect compensation method, and the anti-self-excitation circuit includes capacitors C5 and C7; the output end and input end of the primary amplifier circuit and the secondary amplifier circuit are connected through capacitors C5 and C7 respectively; the voltage negative feedback circuit connects the output end of the push-pull amplifier circuit with the reverse input end of the secondary amplifier circuit through the resistor R9; the input voltage is also input into the push-pull amplifier circuit; The positive input terminal of the first amplifier U1 is grounded via resistor R5, the negative input terminal of the first amplifier U1 is connected to the output signal of the D / A conversion circuit via resistor R3, the output terminal of the first amplifier U1 is respectively connected to the first end of the current limiting resistor R7 and the second end of the resistor R4; the first end of the resistor R4 is connected to the negative input terminal of the first amplifier U1; the second end of the current limiting resistor R7 is connected to the negative input terminal of the second amplifier U2 via the DC blocking capacitor C6; the negative input terminal of the second amplifier U2 is respectively connected to the first end of the resistor R8, the first end of the resistor R9, and the first end of the capacitor C7; the positive input terminal of the second amplifier U2 is grounded via resistor R6; the output terminal of the second amplifier U2 is connected to the second end of the capacitor C7; the second end of the resistor R8 is grounded; the second end of the resistor R9 is connected to the output terminal of the entire excitation AC source.

6. The digital frequency modulation excitation AC source according to claim 5, characterized in that: The push-pull amplifier circuit includes a resistor R11, a resistor R12, a resistor R13, a resistor R14, a capacitor C8, a capacitor C9, a diode D1, a diode D2, a transistor Q1 and a transistor Q2; the resistor R13 and the resistor R14 are power resistors; The overcurrent protection circuit includes a resistor R13, a resistor R14, a diode D3, a diode D4, a transistor Q3 and a transistor Q4; the bases of the control-end transistor Q3 and the transistor Q4 of the overcurrent protection circuit are connected to the output end of the push-pull amplifier circuit through the resistor R13 and the resistor R14 respectively; The first end of the resistor R11, the first end of the capacitor C9 and the collector of the transistor C1 are all connected to the positive end of the power supply; the second end of the resistor R11 is connected to the anode of the diode D1; the cathode of the diode D1 is connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the first end of the resistor R12; the second end of the resistor R12, the second end of the capacitor C8 and the collector of the transistor Q3 are all connected to the negative end of the power supply; the second end of the capacitor C9 is respectively connected to the second end of the resistor R11, the anode of the diode D3, and the base of the transistor Q1; the cathode of the diode D3 is connected to the collector of the transistor Q3; the base of the transistor Q3 is respectively connected to the emitter of the transistor Q1, the cathode of the resistor R11 and the collector of the transistor Q3; the cathode of the diode D3 is connected to the collector of the transistor Q3; the cathode of the transistor Q3 is respectively connected to the emitter of the transistor Q1, the cathode of the resistor R12 and the collector of the transistor Q3; the cathode of the diode D3 is connected to the collector of the transistor Q3; the cathode ... diode D2 and the collector of the transistor Q3; the cathode of the transistor 13 is connected to the first end of the resistor R13; the emitter of the transistor Q3 is connected to the second end of the resistor R13 and the emitter of the transistor Q4 respectively; the collector of the transistor Q4 is connected to the anode of the diode D4, and the base of the transistor Q4 is connected to the second end of the resistor R14 and the emitter of the transistor Q2 respectively; the cathode of the diode D4 is connected to the first end of the capacitor C8, the first end of the resistor R12, the cathode of the diode D2, and the base of the transistor Q2 respectively; the emitter of the transistor Q1 is connected to the first end of the resistor R13, the second end of the resistor R13 is connected to the first end of the resistor R14, and the second end of the resistor R14 is connected to the emitter of the transistor Q2.

7. The digital frequency modulation excitation AC source according to claim 4, characterized in that: The digital processor adopts FPGA.

8. The digital frequency modulation excitation AC source according to claim 6, characterized in that: The resistor R11 and the resistor R12 are current limiting resistors; the resistor R13 and the resistor R14 are power resistors; The diode D1 and the diode D2 are high-speed switching diodes; The transistor Q1 and the transistor Q2 are Darlington transistors; the transistor Q3 and the transistor Q4 are thyristors.

9. The working method of the digital frequency modulation excitation AC source according to claim 8, characterized in that: The method comprises the following steps: S1, the input voltage is converted into the supply voltage of the digital signal processing circuit through the voltage adjustment circuit; S2, after receiving the square wave signal, the digital signal processing circuit outputs a sinusoidal digital signal, which is converted into an analog signal through a D / A conversion circuit to form a sinusoidal fundamental wave signal; S3, the fundamental sine wave signal is amplified by the first-stage amplifier circuit, and then the negative voltage feedback and stable amplification factor processing are performed by the second-stage amplifier circuit to output the sine signal; S4, the sinusoidal signal output by the secondary amplifier circuit is amplified by the push-pull amplifier circuit to output the required excitation AC signal; S5. When the circuit is overloaded, a large current is generated, and the voltage across the resistors R13 and R14 increases, reaching the turn-on voltage of the transistors Q3 and Q4; the overcurrent protection circuit starts to work, and the output of the amplifier circuit is cut off to protect the subsequent circuit; the anti-self-excitation circuit prevents the circuit from generating self-excitation oscillation, and is used to make the output excitation signal more stable.

10. The working method of the digital frequency modulation excitation AC source according to claim 9, characterized in that: In step S2, the digital signal processing circuit outputs a sinusoidal digital signal after receiving the square wave signal, and the sinusoidal digital signal is converted into an analog signal by a D / A conversion circuit to form a sinusoidal fundamental signal, including: S21, using a digital processor to perform frequency division counting on the input square wave signal, determine the frequency of the sine wave, and output a sine signal; S22, using the IP core of the digital processor to establish a memory, digitally encode the standard sinusoidal signal; sampling a period of the sinusoidal signal, and the corresponding sinusoidal output is represented by a decimal value; at the same time, encoding the address, using a hexadecimal number to represent it, so that the address and the output sinusoidal value form a mapping relationship, constructing a sine table, and storing the sine table in the memory; S23, using the pulse signal generated by the active crystal oscillator of the digital processor as the clock base frequency, performing serial data shift and storage on the sinusoidal signal, and outputting the sinusoidal digital value; S24. The sine table in the memory is converted into an analog sine waveform through a D / A conversion circuit to generate an excitation signal of a corresponding frequency, thereby forming a sine fundamental wave signal.

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