Optimized PWM (Pulse Width Modulation) method for improving working efficiency of voltage type inverter

Abstract

The invention discloses an optimized PWM (Pulse Width Modulation) method for improving the working efficiency of a voltage type inverter. The method comprises the following steps that: a single chip microcomputer determines expected voltages ua, ub and uc output by the voltage type inverter according to the control requirement of a previous stage; the single-chip microcomputer calculates three variables ta, tb and tc after collecting a direct current side voltage value ud of the voltage type inverter; the ta, the tb and the tc are corrected; determining a variable value; switching pulses of two adjacent Ts are adjusted, the switching state in the odd number Ts is first 0 and then 1, the switching state in the even number Ts is first 1 and then 0, and a new three-phase PWM oscillogram is obtained. According to the method, the complexity of a PWM algorithm is reduced, an arithmetic unit in the single-chip microcomputer is saved, and the single-chip microcomputer with general performance can complete the algorithm in real time; the switching frequency and the switching loss of the inverter are reduced, the electrical efficiency of the inverter is improved, and the endurance mileage of an electric automobile and the like is prolonged.

Description

Technical Field

[0001] The present invention relates to an optimization method for the operating efficiency of a high-voltage power electronic inverter, and particularly to an optimized PWM method for improving the operating efficiency of a voltage-source inverter. Background Art

[0002] In the current field of power electronics technology, for voltage-source inverter devices, most of them adopt PWM control technology, and the SVPWM algorithm among them is the most typical. Various PWM algorithms need to be calculated in real time in a single-chip microcomputer or a digital signal processor (DSP). The main disadvantages of the current PWM algorithms are as follows:

[0003] 1. The implementation algorithm of PWM is relatively complex and occupies a large amount of computing resources in the single-chip microcomputer;

[0004] 2. At a limited switching frequency, the existing PWM methods result in a relatively high switching frequency and high switching losses of the inverter.

[0005] Therefore, there is an urgent need for an optimized PWM method for improving the operating efficiency of a voltage-source inverter. Summary of the Invention

[0006] Object of the Invention: The object of the present invention is to provide an optimized PWM method for improving the operating efficiency of a voltage-source inverter.

[0007] Technical Solution: The optimized PWM method for improving the operating efficiency of a voltage-source inverter according to the present invention includes the following steps:

[0008] (1) The single-chip microcomputer determines the desired voltages ua, ub, and uc output by the voltage-source inverter according to the control requirements of the previous stage;

[0009] (2) After the single-chip microcomputer collects the DC-side voltage value ud of the voltage-source inverter, it calculates three variables ta, tb, and tc;

[0010] (3) Correct ta, tb, and tc;

[0011] (4) Determine the variable values;

[0012] (5) Adjust the switching pulses of two adjacent Ts. The switching state within odd Ts is first 0 and then 1, and the switching state within even Ts is first 1 and then 0, to obtain a new three-phase PWM waveform diagram.

[0013] Further, in the step (1), the desired voltages ua, ub, and uc satisfy the formula (1):

[0014] ua + ub + uc = 0 (1)

[0015] Further, the calculation formula of step (2) is as follows, where Ts is the switching period, which is the reciprocal of the switching frequency:

[0016] ta = Ts * ua / (ud / 2), tb = Ts * ub / (ud / 2), tc = Ts * uc / (ud / 2) (2)

[0017] Further, the correction formula of step (3) is as follows

[0018] ton_a = ta + dt, ton_b = tb + dt, ton_c = tc + dt (3)

[0019] Further, the formula for the variable values in step (4) is as follows

[0020] dt = Ts - max(ta, tb, tc) (4)

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. Reduce the complexity of the PWM algorithm, save the arithmetic unit inside the single-chip microcomputer, and enable a general-performance single-chip microcomputer to complete this algorithm in real time;

[0023] 2. Reduce the switching frequency and the switching loss of the inverter, improve the electrical efficiency of the inverter, and is beneficial to extending the battery life of electric vehicles, etc. Description of the Drawings

[0024] Figure 1 is the waveform diagram of the traditional SVPWM method;

[0025] Figure 2 is the waveform diagram of the corrected SVPWM method;

[0026] Figure 3 is the new three-phase PWM waveform diagram of the present invention. Specific Embodiments

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0028] The optimized PWM method for improving the working efficiency of the voltage source inverter in this embodiment includes the following steps:

[0029] 1. First, the single-chip microcomputer determines the expected voltages ua, ub, and uc output by the voltage source inverter according to the control requirements of the previous stage, and they satisfy formula (1);

[0030] ua + ub + uc = 0 (1)

[0031] 2. After the microcontroller samples the DC-side voltage value ud of the voltage-source inverter, three variables ta, tb, and tc are calculated as shown in Equation (1). In the equation, Ts is the switching period, which is the reciprocal of the switching frequency.

[0032] ta = Ts * ua / (ud / 2), tb = Ts * ub / (ud / 2), tc = Ts * uc / (ud / 2) (2)

[0033] 3. The values of ta, tb, and tc in Equation (2) may be positive or negative, and need to be corrected according to Equation (3) as the time reference quantity.

[0034] ton_a = ta + dt, ton_b = tb + dt, ton_c = tc + dt (3)

[0035] 4. The value of the dt variable in Equation (3) is taken as follows in Equation (4). The max function in the equation means taking the maximum value of the three variables ta, tb, and tc.

[0036] dt = Ts - max(ta, tb, tc) (4)

[0037] 5. As shown in the example of the classic seven-segment SVPWM waveform diagram, it can be seen that the number of switching times of the three-phase voltage-source inverter within one control period Ts is 2 + 2 + 2 = 6 times. The total switching frequency of the inverter is fs = 6 / Ts. According to the correction in Equation (4), it can be ensured that the switching state of one phase (the highest of the three-phase voltages) is always 1 and remains unchanged. Thus, the number of switching times within one Ts is 0 + 2 + 2 = 4 times, as shown in Figure 1 shown. Figure 2 shown.

[0038] 6. By adjusting the switching pulses of two adjacent Ts, the switching state is 0 first and then 1 within odd Ts, and the switching state is 1 first and then 0 within even Ts. In this way, a new three-phase PWM waveform diagram can be obtained, as shown in Figure 3 shown.

[0039] 7. According to the waveform example of the new PWM method as shown in Figure 3 shown, it can be seen that the total number of switching times within two Ts is 0 + 2 + 2 = 4. Therefore, in this control method, the total switching frequency fs of the inverter is 4 / (2 * Ts) = 2 / Ts, which is only 1 / 3 of the classic SVPWM, thus greatly reducing the switching frequency.

[0040] 8. Among the losses of the inverter, the switching loss accounts for a relatively large proportion. This method can greatly reduce the switching frequency, thereby significantly reducing the switching loss of the inverter, improving the working efficiency of the inverter, and increasing the endurance time and mileage of the system in fields such as electric vehicles.

[0041] The above are only the preferred embodiments of the present invention and do not impose any limitation on the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, which are all within the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. An optimized PWM method for improving the working efficiency of a voltage source inverter, characterized in that: The steps include: (1) The microcontroller determines the expected voltages ua, ub and uc output by the voltage source inverter according to the control requirements of the previous stage; (2) After the single-chip microcomputer collects the DC side voltage value ud of the voltage-type inverter, it calculates three variables ta, tb and tc; (3) Correct ta, tb and tc; (4) Determine the value of the variable; (5) The switch pulses of two adjacent Ts are adjusted. The switch state in the odd Ts is 0 first and then 1, and the switch state in the even Ts is 1 first and then 0, and a new three-phase PWM waveform is obtained.

2. The optimized PWM method for improving the working efficiency of a voltage source inverter according to claim 1, characterized in that: In step (1), the expected voltages ua, ub and uc satisfy equation (1): ua+ub+uc=0 (1).

3. The optimized PWM method for improving the working efficiency of a voltage source inverter according to claim 2, characterized in that: The calculation formula of step (2) is as follows, where Ts is the switching period, which is the reciprocal of the switching frequency: ta=Ts*ua / (ud / 2), tb=Ts*ub / (ud / 2), tc=Ts*uc / (ud / 2) (2).

4. The optimized PWM method for improving the working efficiency of a voltage source inverter according to claim 3, characterized in that: The correction formula of step (3) is as follows: ton_a=ta+dt, ton_b=tb+dt, ton_c=tc+dt (3).

5. The optimized PWM method for improving the working efficiency of a voltage source inverter according to claim 4, characterized in that: The formula for variable values ​​in step (4) is as follows: dt=Ts-max(ta,tb,tc) (4).

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