Ingenieurbüro für EMV

Dipl.-Ing. Heinz Lindenberger

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Double-Inverter

2xPWR-parallel

Double-Inverter with parallel control from a common modulator


- Common use of the DC link capacitor and the Optimized HV-Filter

- Separate winding systems

Double-Inverters are often used together with electric machines with two 3-phase windings.


The two inverters can be interconnected in numerous variations, which, depending on the situation, provide benefits in the ripple voltage, or savings in the DC link capacitance or cancellation effects for switching noise.

FFT-parallel
FFT-1xPWR

HV+        Doppel-Inverter      parallel

HV+        Single-Inverter

The noise level of the parallel-connected Double-Inverter is approx. 6 dB higher than with the Single-Inverter because the switching processes from both converter halves occur exactly at the same time and therefore add up to twice the amplitude

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2xPWR-anti-parallel

Double-Inverter with anti-parallel control from a common modulator


- In one inverter, the gate controls between top and bottom (H and L) are reversed

- Common use of the DC link capacitor and the Optimized HV-Filter

- Separate winding systems

 

FFT-anti-parallel
FFT-anti-parallel-Nullzeiger

HV+        Double-Inverter     anti-parallel

HV+        Double-Inverter     anti-parallel       Null Pointer

The noise level of the anti-parallel Double-Inverter (the switching operations of the two inverter halves are exactly diametrically opposed) does not look especially different, as the parallel Double-Inverter. Only when you set the modulation to zero (null pointer) is the effect clearly visible:

due to the diametrical opposite switching, the common mode noise (CM) largely cancels out (with the exception of certain asymmetries), while the differential mode noise (DM) remains unaffected.

At high modulation rates, the DM noise dominates here after the filter, so that initially no particular difference is noticeable.


This effect can be exploited to save the filter effort for the common mode - or if you want to use or have to use very small Y-Capacitors.


Restrictively, however, one must also point out that for reasons of control strategy, the exact simultaneous switching may not be feasible (which is a prerequisite for the cancellation) and in addition the current direction in anti-parallel control appears exactly mirror-symmetrical to the normal control - and this therefore must be turned on the winding sense of the engine. Furthermore, there is no advantage in terms of the ripple voltage (same as in the normal parallel connection).

 

FFT-anti-parallel-min-Cy

In this simulation, the total capacitance of the Y-Capacitors is reduced to 100 nF


100 nF as the sum of all Y-C on HV + and HV- together


Despite the extremely small Y-Capacity, a very low noise emission can be maintained by the anti-parallel operation

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HV+        Double-Inverter     anti-parallel    

Double-Inverter with 90° phase shifted control from two different modulators


- 2 separate modulators with 90° phase shift

- Common use of the DC link capacitor and the Optimized HV-Filter

- Separate winding systems

 

2xPWR-90°
FFT-90°
FFT-180°
FFT-1xPWR
FFT-1xPWR
2xPWR-180°

HV+        Double-Inverter     90°

HV+        Single-Inverter    

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HV+        Double-Inverter     180°

HV+        Single-Inverter    

Rippel-180°
Rippel-90°
Rippel-Anti-Parallel
Rippel-Parallel
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Double-Inverter with 180° phase shifted control from two different modulators


- 2 separate modulators with 180° phase shift

- Common use of the DC link capacitor and the Optimized HV-Filter

- Separate winding systems

The noise level at the 90° phase shifted Double-Inverter is about 3 dB higher than with the Single-Inverter.


Comparing the spectra, the Double-Inverter lacks the 2nd, 6th, 10th, etc. harmonics


This has a significant effect on the ripple voltage, as shown in the diagrams at the bottom



The noise level at the 180° phase shifted Double-Inverter is about 3 dB higher than with the Single-Inverter.


Comparing the spectra, the Double-Inverter lacks the odd-numbered harmonics


This has a significant effect on the ripple voltage, as shown in the diagrams at the bottom

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Ripple-Voltage       Double-Inverter     parallel        at  m = 1

Ripple-Voltage       Double-Inverter     anti-parallel        at  m = 1

Ripple-Voltage       Double-Inverter     90°        at  m = 1

Ripple-Voltage       Double-Inverter     180°        at  m = 1

The Ripple-Voltage of the parallel operating Double-Inverter is analogous to the ripple voltage of the Single-Inverter - only with twice the current drawn from the DC link.


The Ripple-Voltage of the anti-parallel operating Double-Inverter is just as high. Despite the anti-parallel operation, the current is drawn from the DC link in the same time by both inverters. However, the current direction in the motor cable is opposite – as can be seen directly from the diagram.


In the case of the 90° inverter, the ripple voltage peaks are folded inwards, resulting in approximately half the maximum amplitude compared to the parallel or anti-parallel working inverter.



The Voltage-Ripple of the 180° inverter is dramatically lower:  The maximum amplitude here is only about 15 Vpp - while it reaches about 80 Vpp for the parallel inverter and about 40 Vpp for the 90° inverter.

© Ingenieurbüro Lindenberger       8447