A simple and practical vehicle-mounted sine wave inverter power supply

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A simple and practical vehicle-mounted sine wave inverter power supply [Copy link]

Abstract: This paper introduces a simple and practical vehicle-mounted sine wave inverter power supply. The control circuit uses a weighted resistor network sine wave generator and a dedicated control chip UC3637 to generate SPWM waves, which are transmitted to the gate of the inverter circuit power switch via a high-voltage suspension driver IR2110. The experimental results show that the output waveform of the power supply is good and the power supply characteristics meet the requirements. Its outstanding advantages are simple structure, low cost and high reliability.
Keywords: weighted resistor; UC3637; IR2110; SPWM; inverter power supply
Classification number: TN86 Document code: A Article number: 0219-2713(2005)05-0024-04

0 Introduction
Power supplies of different specifications are equipped in some transportation, field measurement and control, mobile weapons and equipment, engineering repair vehicles and other equipment. Usually, these equipment have a small working space, a harsh environment and large interference. Therefore, the design requirements for the power supply are also very high. In addition to having good electrical performance, it must also have the characteristics of small size, light weight, low cost, high reliability and strong anti-interference. Aiming at the specific requirements of a certain mobile device, a simple and practical on-board sinusoidal wave inverter power supply is developed, which adopts the SPWM working mode and forms the entire circuit with the simplest hardware configuration and the most common devices. Experiments have proved that the power supply has the characteristics of simple circuit, low cost and high reliability, which meets the actual requirements. This paper introduces the working principle of each part, focusing on the design of the reference sine generator and high-voltage suspension drive circuit.

1 System composition
The system composition block diagram is shown in Figure 1. The programmable gain amplifier composed of a weighted resistor network and an integrated operational amplifier generates a step wave reference sine wave, and UC3637 is used as a sine pulse width modulator. The generated SPWM wave is sent to the gate of the upper and lower bridge arm power switches of the inverter circuit (half-bridge) after passing through a dedicated high-voltage suspension driver IR211O. The output of the inverter circuit is filtered and isolated to obtain the output voltage u0. u0 is provided as the control voltage of the reference sine generator after passing through the PI regulator, and the amplitude of the reference sine wave (i.e., adjusting ma) is adjusted to achieve the purpose of adjusting the output voltage. The topology of the inverter main circuit is shown in Figure 2, which is a conventional half-bridge circuit.

2 Control Circuit
From the SPWM working mode, the control circuit must generate two basic signals, namely the reference sine wave modulation signal and the triangular wave carrier signal, and send the modulation wave and the carrier to the sine pulse width modulation circuit to generate the SPWM pulse wave, and the drive circuit controls the corresponding power switch module in the main circuit.
2.1 Sine modulation wave generation circuit
The sine modulation wave generation circuit is shown in Figure 3. CD4067 is a 16-to-1 analog switch. R1~R8 are weighted resistors (referred to as "weighted resistors"), whose values are related to the sampling time ωti, and i is the sampling sequence number.

In order to facilitate time quantization and digital control sampling, as well as to take into account the operating frequency of the power device, mf is selected as an integer and an even number. For example, mf = 30. The desired output frequency f8 (i.e., modulation frequency) is 400Hz, then the switching frequency of the device f8 = 12kHz, within the preferred operating frequency of the IGBT, in view of the symmetry of the sine wave. Only the weighted resistance of T/4 (T is the period of the modulation wave) is calculated, i.e., t. It is not difficult to understand that R8 is the weighted resistance value when ωti = 90°, and it is symmetrical on both sides with R8 as the center in the half cycle, and the connection relationship is shown in Figure 3. There are 15 samplings in the half cycle, and CD4016l is a preset 4-bit binary add counter. It can be preset to 1 first, and automatically reset when 15 times are recorded, and preset to 1 at the same time.
From the above analysis, it is known that U1A is a programmable gain amplifier, and the gain Kp = -Rf/Rk. The size of Kp is different when the serial number of Rk is different. A series of 15-step half-wave sine can be obtained at the output end of U1A, and then the polarity conversion circuit U1B (where R10=Rk12) can obtain a complete sine modulation wave ur with symmetry between positive and negative half cycles.
2.2 Triangle carrier and clock generation circuit
UC3637 contains a triangle wave oscillator. The voltage divider points +VTH and -VTH of R20, R21, and R22 in Figure 4 are the turning voltages of the positive peak and negative peak of the triangle wave. The oscillation frequency fs of the triangle wave is jointly determined by ±VTH, CT, and RT, and the relationship is as follows:

There is a constant current source inside UC3637 to provide charging and discharging current for CT. A triangle wave with symmetric positive and negative slopes and good linearity is generated at pin 2. The triangle wave is sent to the in-phase terminal pin 15 of the internal op amp. It is then output from pins 16 and 17. It is then sent to pins 8 and 10 of the two sinusoidal pulse width modulators through R23 and R24 respectively. Adjusting Rp can adjust the carrier frequency, and due to synchronous modulation (mf=30), it also changes the output frequency within a certain range.

Since UC3637 has no synchronous signal output terminal, a signal conditioning circuit is designed to convert the triangular wave carrier signal into a clock signal, which is used as the counting clock of CD40161, that is, the reference sine sampling pulse. The first stage of the conditioning circuit is an active differential circuit, which consists of U1D and surrounding resistors and capacitors. C1 and R27 are differential capacitors and resistors; R26 and C2 eliminate high-frequency oscillations; R26 < R27, C2 < C1. U1D outputs a bipolar square wave signal, which is then compared by U2 (comparator) to output a clock signal that matches the level of the subsequent logic circuit (CD40161).
2.3 Sine pulse width modulator
There are two independent comparators in UC3637, and their input and output terminals are respectively led to the outside of the chip, which is quite flexible in application. As mentioned above, the triangular wave carrier is sent to pins 8 and 10 of the two comparators by R23 and R24. Then, the modulation wave generated by the reference sine wave generating circuit is sent to the pin 9 and pin 11 of the two comparators by R18 and R19 respectively. Pin 9 and pin 11 are also connected to the ±Vs power supply by resistors R16 and R17 respectively. The bias level ±VT obtained thereby determines the dead time td of the upper and lower power switch devices [see formula (3)]. The two modulators output SPWM control signals through pin 4 and pin 7 respectively.

td=[(+VT/2)-(-VT/2)]Ts/2VTH (3)

Where: Ts is the switching period.

3 High-voltage suspension drive circuit
The IR2110 driver produced by IR has the advantages of both optocoupler isolation (small size) and electromagnetic isolation (fast speed), and is the preferred driver device in small power conversion devices. The circuit of IR2110 driving the half-bridge inverter is shown in Figure 5.

In the figure, VD1 and C1 are the bootstrap diode and bootstrap capacitor. VD1 must use a fast recovery diode with the same withstand voltage level as the power switch. The design of the bootstrap capacitor is also crucial. The withstand voltage of C1 must be higher than the driving voltage required when the power device is fully turned on (10V, the undervoltage lockout voltage on the high-voltage side is 8.7V/8.3V); if there is a 1.5V voltage drop on the charging path of C1, and it is assumed that half of the gate voltage is reduced due to leakage, the bootstrap capacitor C1 can be selected according to formula (4).


In the formula: Qg is the gate charge of the IGBT.
In engineering applications, C1>2Q/(Vcc-10-1.5) should be taken, and a non-inductive capacitor with stable capacity and pulse current resistance should be selected. The detailed design of the bootstrap capacitor can be referred to reference [3].

4 Experimental results
Design example: main circuit half-bridge topology, SPWM working mode. Input Ud=270(1±10%)V DC voltage; output sine wave AC voltage Uo=115V, 400Hz. 500W, switching frequency 12kHz; filter inductor 2mH, filter capacitor 10μF; power switch uses IGBT single tube 1MBH5OD-060; the main integrated circuits used in the control circuit are UC3637, CD4067, CD40161, TL084, 1 piece each: drive circuit 1 piece IR2110. Figures 6 to 8 are experimental waveforms. THD<3%.

　

5 Conclusion
The vehicle-mounted inverter power supply introduced in this article has the characteristics of simplicity, practicality, low cost and high reliability. Moreover, the overall weight and size of the power supply are light, which meets the needs of mobile equipment and vehicles. It has been successfully applied to a frequently moving military equipment.

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